Instruction and Logic for Detecting Numeric Accumulation Error

ABSTRACT

A processor includes circuitry to decode at least one instruction and an execution unit. The decoded instruction may compute a floating point result. The execution unit includes circuitry to execute the instruction to determine the floating point result, compute the amount of precision lost in a mantissa of the floating point result, compare the amount of precision lost to a numeric accumulation error precision threshold, determine whether a numeric accumulation error occurred based on the comparison, and write a value to a flag. The amount of precision lost corresponds to a plurality of bits lost in the mantissa of the floating point result. The value to be written to the flag may be based on the determination that the numeric accumulation error occurred. The flag may be for notification that the numeric accumulation error occurred.

FIELD OF THE INVENTION

The present disclosure pertains to the field of processing logic, microprocessors, and associated instruction set architecture that, when executed by the processor or other processing logic, perform logical, mathematical, or other functional operations.

DESCRIPTION OF RELATED ART

Multiprocessor systems are becoming more and more common. Applications of multiprocessor systems include dynamic domain partitioning all the way down to desktop computing. In order to take advantage of multiprocessor systems, code to be executed may be separated into multiple threads for execution by various processing entities. Each thread may be executed in parallel with one another. Instructions as they are received on a processor may be decoded into terms or instruction words that are native, or more native, for execution on the processor. Processors may be implemented in a system on a chip. Floating point numbers may be added, subtracted, or multiplied. Such floating point operations may be used in deep learning mathematical simulations.

DESCRIPTION OF THE FIGURES

Embodiments are illustrated by way of example and not limitation in the Figures of the accompanying drawings:

FIG. 1A is a block diagram of an exemplary computer system formed with a processor that may include execution units to execute an instruction, in accordance with embodiments of the present disclosure;

FIG. 1B illustrates a data processing system, in accordance with embodiments of the present disclosure;

FIG. 1C illustrates other embodiments of a data processing system for performing text string comparison operations;

FIG. 2 is a block diagram of the micro-architecture for a processor that may include logic circuits to perform instructions, in accordance with embodiments of the present disclosure;

FIG. 3A illustrates various packed data type representations in multimedia registers, in accordance with embodiments of the present disclosure;

FIG. 3B illustrates possible in-register data storage formats, in accordance with embodiments of the present disclosure;

FIG. 3C illustrates various signed and unsigned packed data type representations in multimedia registers, in accordance with embodiments of the present disclosure;

FIG. 3D illustrates an embodiment of an operation encoding format;

FIG. 3E illustrates another possible operation encoding format having forty or more bits, in accordance with embodiments of the present disclosure;

FIG. 3F illustrates yet another possible operation encoding format, in accordance with embodiments of the present disclosure;

FIG. 4A is a block diagram illustrating an in-order pipeline and a register renaming stage, out-of-order issue/execution pipeline, in accordance with embodiments of the present disclosure;

FIG. 4B is a block diagram illustrating an in-order architecture core and a register renaming logic, out-of-order issue/execution logic to be included in a processor, in accordance with embodiments of the present disclosure;

FIG. 5A is a block diagram of a processor, in accordance with embodiments of the present disclosure;

FIG. 5B is a block diagram of an example implementation of a core, in accordance with embodiments of the present disclosure;

FIG. 6 is a block diagram of a system, in accordance with embodiments of the present disclosure;

FIG. 7 is a block diagram of a second system, in accordance with embodiments of the present disclosure;

FIG. 8 is a block diagram of a third system in accordance with embodiments of the present disclosure;

FIG. 9 is a block diagram of a system-on-a-chip, in accordance with embodiments of the present disclosure;

FIG. 10 illustrates a processor containing a central processing unit and a graphics processing unit which may perform at least one instruction, in accordance with embodiments of the present disclosure;

FIG. 11 is a block diagram illustrating the development of IP cores, in accordance with embodiments of the present disclosure;

FIG. 12 illustrates how an instruction of a first type may be emulated by a processor of a different type, in accordance with embodiments of the present disclosure;

FIG. 13 illustrates a block diagram contrasting the use of a software instruction converter to convert binary instructions in a source instruction set to binary instructions in a target instruction set, in accordance with embodiments of the present disclosure;

FIG. 14 is a block diagram of an instruction set architecture of a processor, in accordance with embodiments of the present disclosure;

FIG. 15 is a more detailed block diagram of an instruction set architecture of a processor, in accordance with embodiments of the present disclosure;

FIG. 16 is a block diagram of an execution pipeline for an instruction set architecture of a processor, in accordance with embodiments of the present disclosure;

FIG. 17 is a block diagram of an electronic device for utilizing a processor, in accordance with embodiments of the present disclosure;

FIG. 18 is a block diagram of a system for detecting numeric accumulation error, in accordance with embodiments of the present disclosure;

FIG. 19A is a block diagram of a floating point unit for accumulating floating point numbers, in accordance with embodiments of the present disclosure;

FIG. 19B is a block diagram of an execution unit for detecting numeric accumulation error in floating point numbers with aligned exponents, in accordance with embodiments of the present disclosure; and

FIG. 20 is a diagram of operation of a method for detecting numeric accumulation error, in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

The following description describes an instruction and processing logic for detecting numeric accumulation error. The instruction and processing logic may be implemented on an out-of-order processor. In the following description, numerous specific details such as processing logic, processor types, micro-architectural conditions, events, enablement mechanisms, and the like are set forth in order to provide a more thorough understanding of embodiments of the present disclosure. It will be appreciated, however, by one skilled in the art that the embodiments may be practiced without such specific details. Additionally, some well-known structures, circuits, and the like have not been shown in detail to avoid unnecessarily obscuring embodiments of the present disclosure.

Although the following embodiments are described with reference to a processor, other embodiments are applicable to other types of integrated circuits and logic devices. Similar techniques and teachings of embodiments of the present disclosure may be applied to other types of circuits or semiconductor devices that may benefit from higher pipeline throughput and improved performance. The teachings of embodiments of the present disclosure are applicable to any processor or machine that stores data to memory. However, the embodiments are not limited to processors or machines that perform 512-bit, 256-bit, 128-bit, 64-bit, 32-bit, or 16-bit data operations and may be applied to any processor and machine in which manipulation or management of data may be performed. In addition, the following description provides examples, and the accompanying drawings show various examples for the purposes of illustration. However, these examples should not be construed in a limiting sense as they are merely intended to provide examples of embodiments of the present disclosure rather than to provide an exhaustive list of all possible implementations of embodiments of the present disclosure.

Although the below examples describe instruction handling and distribution in the context of execution units and logic circuits, other embodiments of the present disclosure may be accomplished by way of a data or instructions stored on a machine-readable, tangible medium, which when performed by a machine cause the machine to perform functions consistent with at least one embodiment of the disclosure. In one embodiment, functions associated with embodiments of the present disclosure are embodied in machine-executable instructions. The instructions may be used to cause a general-purpose or special-purpose processor that may be programmed with the instructions to perform the steps of the present disclosure. Embodiments of the present disclosure may be provided as a computer program product or software which may include a machine or computer-readable medium having stored thereon instructions which may be used to program a computer (or other electronic devices) to perform one or more operations according to embodiments of the present disclosure. Furthermore, steps of embodiments of the present disclosure might be performed by specific hardware components that contain fixed-function logic for performing the steps, or by any combination of programmed computer components and fixed-function hardware components. Throughout this disclosure, unless explicitly stated otherwise, a compound form of a reference numeral refers to the element generically or collectively. Thus, for example, widget 101A or 101-1 refers to an instance of a widget class, which may be referred to collectively as widgets 101 and any one of which may be referred to generically as widget 101.

Instructions used to program circuitry to perform embodiments of the present disclosure may be stored within a memory in the system, such as DRAM, cache, flash memory, or other storage. Furthermore, the instructions may be distributed via a network or by way of other computer-readable media. Thus a machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer), but is not limited to, floppy diskettes, optical disks, Compact Disc, Read-Only Memory (CD-ROMs), and magneto-optical disks, Read-Only Memory (ROMs), Random Access Memory (RAM), Erasable Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), magnetic or optical cards, flash memory, or a tangible, machine-readable storage used in the transmission of information over the Internet via electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Accordingly, the computer-readable medium may include any type of tangible machine-readable medium suitable for storing or transmitting electronic instructions or information in a form readable by a machine (e.g., a computer).

A design may go through various stages, from creation to simulation to fabrication. Data representing a design may represent the design in a number of manners. First, as may be useful in simulations, the hardware may be represented using a hardware description language or another functional description language. Additionally, a circuit level model with logic and/or transistor gates may be produced at some stages of the design process. Furthermore, designs, at some stage, may reach a level of data representing the physical placement of various devices in the hardware model. In cases wherein some semiconductor fabrication techniques are used, the data representing the hardware model may be the data specifying the presence or absence of various features on different mask layers for masks used to produce the integrated circuit. In any representation of the design, the data may be stored in any form of a machine-readable medium. A memory or a magnetic or optical storage such as a disc may be the machine-readable medium to store information transmitted via optical or electrical wave modulated or otherwise generated to transmit such information. When an electrical carrier wave indicating or carrying the code or design is transmitted, to the extent that copying, buffering, or retransmission of the electrical signal is performed, a new copy may be made. Thus, a communication provider or a network provider may store on a tangible, machine-readable medium, at least temporarily, an article, such as information encoded into a carrier wave, embodying techniques of embodiments of the present disclosure.

In modern processors, a number of different execution units may be used to process and execute a variety of code and instructions. Some instructions may be quicker to complete while others may take a number of clock cycles to complete. The faster the throughput of instructions, the better the overall performance of the processor. Thus it would be advantageous to have as many instructions execute as fast as possible. However, there may be certain instructions that have greater complexity and require more in terms of execution time and processor resources, such as floating point instructions, load/store operations, data moves, etc.

As more computer systems are used in internet, text, and multimedia applications, additional processor support has been introduced over time. In one embodiment, an instruction set may be associated with one or more computer architectures, including data types, instructions, register architecture, addressing modes, memory architecture, interrupt and exception handling, and external input and output (I/O).

In one embodiment, the instruction set architecture (ISA) may be implemented by one or more micro-architectures, which may include processor logic and circuits used to implement one or more instruction sets. Accordingly, processors with different micro-architectures may share at least a portion of a common instruction set. For example, Intel® Pentium 4 processors, Intel® Core™ processors, and processors from Advanced Micro Devices, Inc. of Sunnyvale Calif. implement nearly identical versions of the x86 instruction set (with some extensions that have been added with newer versions), but have different internal designs. Similarly, processors designed by other processor development companies, such as ARM Holdings, Ltd., MIPS, or their licensees or adopters, may share at least a portion a common instruction set, but may include different processor designs. For example, the same register architecture of the ISA may be implemented in different ways in different micro-architectures using new or well-known techniques, including dedicated physical registers, one or more dynamically allocated physical registers using a register renaming mechanism (e.g., the use of a Register Alias Table (RAT), a Reorder Buffer (ROB) and a retirement register file. In one embodiment, registers may include one or more registers, register architectures, register files, or other register sets that may or may not be addressable by a software programmer.

An instruction may include one or more instruction formats. In one embodiment, an instruction format may indicate various fields (number of bits, location of bits, etc.) to specify, among other things, the operation to be performed and the operands on which that operation will be performed. In a further embodiment, some instruction formats may be further defined by instruction templates (or sub-formats). For example, the instruction templates of a given instruction format may be defined to have different subsets of the instruction format's fields and/or defined to have a given field interpreted differently. In one embodiment, an instruction may be expressed using an instruction format (and, if defined, in a given one of the instruction templates of that instruction format) and specifies or indicates the operation and the operands upon which the operation will operate.

Scientific, financial, auto-vectorized general purpose, RMS (recognition, mining, and synthesis), and visual and multimedia applications (e.g., 2D/3D graphics, image processing, video compression/decompression, voice recognition algorithms and audio manipulation) may require the same operation to be performed on a large number of data items. In one embodiment, Single Instruction Multiple Data (SIMD) refers to a type of instruction that causes a processor to perform an operation on multiple data elements. SIMD technology may be used in processors that may logically divide the bits in a register into a number of fixed-sized or variable-sized data elements, each of which represents a separate value. For example, in one embodiment, the bits in a 64-bit register may be organized as a source operand containing four separate 16-bit data elements, each of which represents a separate 16-bit value. This type of data may be referred to as ‘packed’ data type or ‘vector’ data type, and operands of this data type may be referred to as packed data operands or vector operands. In one embodiment, a packed data item or vector may be a sequence of packed data elements stored within a single register, and a packed data operand or a vector operand may a source or destination operand of a SIMD instruction (or ‘packed data instruction’ or a ‘vector instruction’). In one embodiment, a SIMD instruction specifies a single vector operation to be performed on two source vector operands to generate a destination vector operand (also referred to as a result vector operand) of the same or different size, with the same or different number of data elements, and in the same or different data element order.

SIMD technology, such as that employed by the Intel® Core™ processors having an instruction set including x86, MMX™, Streaming SIMD Extensions (SSE), SSE2, SSE3, SSE4.1, and SSE4.2 instructions, ARM processors, such as the ARM Cortex® family of processors having an instruction set including the Vector Floating Point (VFP) and/or NEON instructions, and MIPS processors, such as the Loongson family of processors developed by the Institute of Computing Technology (ICT) of the Chinese Academy of Sciences, has enabled a significant improvement in application performance (Core™ and MMX™ are registered trademarks or trademarks of Intel Corporation of Santa Clara, Calif.).

In one embodiment, destination and source registers/data may be generic terms to represent the source and destination of the corresponding data or operation. In some embodiments, they may be implemented by registers, memory, or other storage areas having other names or functions than those depicted. For example, in one embodiment, “DEST1” may be a temporary storage register or other storage area, whereas “SRC1” and “SRC2” may be a first and second source storage register or other storage area, and so forth. In other embodiments, two or more of the SRC and DEST storage areas may correspond to different data storage elements within the same storage area (e.g., a SIMD register). In one embodiment, one of the source registers may also act as a destination register by, for example, writing back the result of an operation performed on the first and second source data to one of the two source registers serving as a destination registers.

FIG. 1A is a block diagram of an exemplary computer system formed with a processor that may include execution units to execute an instruction, in accordance with embodiments of the present disclosure. System 100 may include a component, such as a processor 102 to employ execution units including circuits with logic to perform algorithms for process data, in accordance with the present disclosure, such as in the embodiment described herein. System 100 may be representative of processing systems based on the PENTIUM® III, PENTIUM® 4, Xeon™, Itanium®, XScale™ and/or StrongARM™ microprocessors available from Intel Corporation of Santa Clara, Calif., although other systems (including PCs having other microprocessors, engineering workstations, set-top boxes and the like) may also be used. In one embodiment, sample system 100 may execute a version of the WINDOWS' operating system available from Microsoft Corporation of Redmond, Wash., although other operating systems (UNIX and Linux for example), embedded software, and/or graphical user interfaces, may also be used. Thus, embodiments of the present disclosure are not limited to any specific combination of hardware circuitry, programmable circuitry, and software.

Embodiments are not limited to computer systems. Embodiments of the present disclosure may be used in other devices such as handheld devices and embedded applications. Some examples of handheld devices include cellular phones, Internet Protocol devices, digital cameras, personal digital assistants (PDAs), and handheld PCs. Embedded applications may include a micro controller, a digital signal processor (DSP), system on a chip, network computers (NetPC), set-top boxes, network hubs, wide area network (WAN) switches, or any other system that may perform one or more instructions in accordance with at least one embodiment.

Computer system 100 may include a processor 102 that may include one or more execution units 108 to perform an algorithm to perform at least one instruction in accordance with one embodiment of the present disclosure. One embodiment may be described in the context of a single processor desktop or server system, but other embodiments may be included in a multiprocessor system. System 100 may be an example of a ‘hub’ system architecture. System 100 may include a processor 102 for processing data signals. Processor 102 may include a complex instruction set computer (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a processor implementing a combination of instruction sets, or any other processor device, such as a digital signal processor, for example. In one embodiment, processor 102 may be coupled to a processor bus 110 that may transmit data signals between processor 102 and other components in system 100. The elements of system 100 may perform conventional functions that are well known to those familiar with the art.

In one embodiment, processor 102 may include a Level 1 (L1) internal cache memory 104. Depending on the architecture, the processor 102 may have a single internal cache or multiple levels of internal cache. In another embodiment, the cache memory may reside external to processor 102. Other embodiments may also include a combination of both internal and external caches depending on the particular implementation and needs. Register file 106 may store different types of data in various registers including integer registers, floating point registers, status registers, and instruction pointer register.

Execution unit 108, including circuits with logic to perform integer and floating point operations, also resides in processor 102. Processor 102 may also include a microcode (ucode) ROM that stores microcode for certain macroinstructions. In one embodiment, execution unit 108 may include circuits with logic to handle a packed instruction set 109. By including the packed instruction set 109 in the instruction set of a general-purpose processor 102, along with associated circuitry to execute the instructions, the operations used by many multimedia applications may be performed using packed data in a general-purpose processor 102. Thus, many multimedia applications may be accelerated and executed more efficiently by using the full width of a processor's data bus for performing operations on packed data. This may eliminate the need to transfer smaller units of data across the processor's data bus to perform one or more operations one data element at a time.

Embodiments of an execution unit 108 may also be used in micro controllers, embedded processors, graphics devices, DSPs, and other types of logic circuits. System 100 may include a memory 120. Memory 120 may be implemented as a dynamic random access memory (DRAM) device, a static random access memory (SRAM) device, flash memory device, or other memory device. Memory 120 may store instructions and/or data represented by data signals that may be executed by processor 102.

A system logic chip 116 may be coupled to processor bus 110 and memory 120. System logic chip 116 may include a memory controller hub (MCH). Processor 102 may communicate with MCH 116 via a processor bus 110. MCH 116 may provide a high bandwidth memory path 118 to memory 120 for instruction and data storage and for storage of graphics commands, data and textures. MCH 116 may direct data signals between processor 102, memory 120, and other components in system 100 and to bridge the data signals between processor bus 110, memory 120, and system I/O 122. In some embodiments, the system logic chip 116 may provide a graphics port for coupling to a graphics controller 112. MCH 116 may be coupled to memory 120 through a memory interface 118. Graphics card 112 may be coupled to MCH 116 through an Accelerated Graphics Port (AGP) interconnect 114.

System 100 may use a proprietary hub interface bus 122 to couple MCH 116 to I/O controller hub (ICH) 130. In one embodiment, ICH 130 may provide direct connections to some I/O devices via a local I/O bus. The local I/O bus may include a high-speed I/O bus for connecting peripherals to memory 120, chipset, and processor 102. Examples may include the audio controller, firmware hub (flash BIOS) 128, wireless transceiver 126, data storage 124, legacy I/O controller containing user input and keyboard interfaces, a serial expansion port such as Universal Serial Bus (USB), and a network controller 134. Data storage device 124 may comprise a hard disk drive, a floppy disk drive, a CD-ROM device, a flash memory device, or other mass storage device.

For another embodiment of a system, an instruction in accordance with one embodiment may be used with a system on a chip. One embodiment of a system on a chip comprises of a processor and a memory. The memory for one such system may include a flash memory. The flash memory may be located on the same die as the processor and other system components. Additionally, other logic blocks such as a memory controller or graphics controller may also be located on a system on a chip.

FIG. 1B illustrates a data processing system 140 which implements the principles of embodiments of the present disclosure. It will be readily appreciated by one of skill in the art that the embodiments described herein may operate with alternative processing systems without departure from the scope of embodiments of the disclosure.

Computer system 140 comprises a processing core 159 for performing at least one instruction in accordance with one embodiment. In one embodiment, processing core 159 represents a processing unit of any type of architecture, including but not limited to a CISC, a RISC or a VLIW type architecture. Processing core 159 may also be suitable for manufacture in one or more process technologies and by being represented on a machine-readable media in sufficient detail, may be suitable to facilitate said manufacture.

Processing core 159 comprises an execution unit 142, a set of register files 145, and a decoder 144. Processing core 159 may also include additional circuitry (not shown) which may be unnecessary to the understanding of embodiments of the present disclosure. Execution unit 142 may execute instructions received by processing core 159. In addition to performing typical processor instructions, execution unit 142 may perform instructions in packed instruction set 143 for performing operations on packed data formats. Packed instruction set 143 may include instructions for performing embodiments of the disclosure and other packed instructions. Execution unit 142 may be coupled to register file 145 by an internal bus. Register file 145 may represent a storage area on processing core 159 for storing information, including data. As previously mentioned, it is understood that the storage area may store the packed data might not be critical. Execution unit 142 may be coupled to decoder 144. Decoder 144 may decode instructions received by processing core 159 into control signals and/or microcode entry points. In response to these control signals and/or microcode entry points, execution unit 142 performs the appropriate operations. In one embodiment, the decoder may interpret the opcode of the instruction, which will indicate what operation should be performed on the corresponding data indicated within the instruction.

Processing core 159 may be coupled with bus 141 for communicating with various other system devices, which may include but are not limited to, for example, synchronous dynamic random access memory (SDRAM) control 146, static random access memory (SRAM) control 147, burst flash memory interface 148, personal computer memory card international association (PCMCIA)/compact flash (CF) card control 149, liquid crystal display (LCD) control 150, direct memory access (DMA) controller 151, and alternative bus master interface 152. In one embodiment, data processing system 140 may also comprise an I/O bridge 154 for communicating with various I/O devices via an I/O bus 153. Such I/O devices may include but are not limited to, for example, universal asynchronous receiver/transmitter (UART) 155, universal serial bus (USB) 156, Bluetooth wireless UART 157 and I/O expansion interface 158.

One embodiment of data processing system 140 provides for mobile, network and/or wireless communications and a processing core 159 that may perform SIMD operations including a text string comparison operation. Processing core 159 may be programmed with various audio, video, imaging and communications algorithms including discrete transformations such as a Walsh-Hadamard transform, a fast Fourier transform (FFT), a discrete cosine transform (DCT), and their respective inverse transforms; compression/decompression techniques such as color space transformation, video encode motion estimation or video decode motion compensation; and modulation/demodulation (MODEM) functions such as pulse coded modulation (PCM).

FIG. 1C illustrates other embodiments of a data processing system that performs SIMD text string comparison operations. In one embodiment, data processing system 160 may include a main processor 166, a SIMD coprocessor 161, a cache memory 167, and an input/output system 168. Input/output system 168 may optionally be coupled to a wireless interface 169. SIMD coprocessor 161 may perform operations including instructions in accordance with one embodiment. In one embodiment, processing core 170 may be suitable for manufacture in one or more process technologies and by being represented on a machine-readable media in sufficient detail, may be suitable to facilitate the manufacture of all or part of data processing system 160 including processing core 170.

In one embodiment, SIMD coprocessor 161 comprises an execution unit 162 and a set of register files 164. One embodiment of main processor 166 comprises a decoder 165A to recognize instructions of instruction set 163 including instructions in accordance with one embodiment for execution by execution unit 162. In other embodiments, SIMD coprocessor 161 also comprises 165B at least part of decoder 165A to decode instructions of instruction set 163. Processing core 170 may also include additional circuitry (not shown) which may be unnecessary to the understanding of embodiments of the present disclosure.

In operation, main processor 166 executes a stream of data processing instructions that control data processing operations of a general type including interactions with cache memory 167, and input/output system 168. Embedded within the stream of data processing instructions may be SIMD coprocessor instructions. Decoder 165A of main processor 166 recognizes these SIMD coprocessor instructions as being of a type that should be executed by an attached SIMD coprocessor 161. Accordingly, main processor 166 issues these SIMD coprocessor instructions (or control signals representing SIMD coprocessor instructions) on the coprocessor bus 171. From coprocessor bus 171, these instructions may be received by any attached SIMD coprocessors. In this case, SIMD coprocessor 161 may accept and execute any received SIMD coprocessor instructions intended for it.

Data may be received via wireless interface 169 for processing by the SIMD coprocessor instructions. For one example, voice communication may be received in the form of a digital signal, which may be processed by the SIMD coprocessor instructions to regenerate digital audio samples representative of the voice communications. For another example, compressed audio and/or video may be received in the form of a digital bit stream, which may be processed by the SIMD coprocessor instructions to regenerate digital audio samples and/or motion video frames. In one embodiment of processing core 170, main processor 166, and a SIMD coprocessor 161 may be integrated into a single processing core 170 comprising an execution unit 162, a set of register files 164, and a decoder 165 to recognize instructions of instruction set 163 including instructions in accordance with one embodiment.

FIG. 2 is a block diagram of the micro-architecture for a processor 200 that may include logic circuits to perform instructions, in accordance with embodiments of the present disclosure. In some embodiments, an instruction in accordance with one embodiment may be implemented to operate on data elements having sizes of byte, word, doubleword, quadword, etc., as well as datatypes, such as single and double precision integer and floating point datatypes. In one embodiment, in-order front end 201 may implement a part of processor 200 that may fetch instructions to be executed and prepares the instructions to be used later in the processor pipeline. Front end 201 may include several units. In one embodiment, instruction prefetcher 226 fetches instructions from memory and feeds the instructions to an instruction decoder 228 which in turn decodes or interprets the instructions. For example, in one embodiment, the decoder decodes a received instruction into one or more operations called “micro-instructions” or “micro-operations” (also called micro op or uops) that the machine may execute. In other embodiments, the decoder parses the instruction into an opcode and corresponding data and control fields that may be used by the micro-architecture to perform operations in accordance with one embodiment. In one embodiment, trace cache 230 may assemble decoded uops into program ordered sequences or traces in uop queue 234 for execution. When trace cache 230 encounters a complex instruction, microcode ROM 232 provides the uops needed to complete the operation.

Some instructions may be converted into a single micro-op, whereas others need several micro-ops to complete the full operation. In one embodiment, if more than four micro-ops are needed to complete an instruction, decoder 228 may access microcode ROM 232 to perform the instruction. In one embodiment, an instruction may be decoded into a small number of micro ops for processing at instruction decoder 228. In another embodiment, an instruction may be stored within microcode ROM 232 should a number of micro-ops be needed to accomplish the operation. Trace cache 230 refers to an entry point programmable logic array (PLA) to determine a correct micro-instruction pointer for reading the micro-code sequences to complete one or more instructions in accordance with one embodiment from micro-code ROM 232. After microcode ROM 232 finishes sequencing micro-ops for an instruction, front end 201 of the machine may resume fetching micro-ops from trace cache 230.

Out-of-order execution engine 203 may prepare instructions for execution. The out-of-order execution logic has a number of buffers to smooth out and re-order the flow of instructions to optimize performance as they go down the pipeline and get scheduled for execution. The allocator logic 215 allocates the machine buffers and resources that each uop needs in order to execute. The register renaming logic 215 renames logic registers onto entries in a register file. The allocator 215 also allocates an entry for each uop in one of the two uop queues, one for memory operations 207 and one for non-memory operations 205, in front of the instruction schedulers: memory scheduler 209, fast scheduler 202, slow/general floating point scheduler 204, and simple floating point scheduler 206. Uop schedulers 202, 204, 206, determine when a uop is ready to execute based on the readiness of their dependent input register operand sources and the availability of the execution resources the uops need to complete their operation. Fast scheduler 202 of one embodiment may schedule on each half of the main clock cycle while the other schedulers may only schedule once per main processor clock cycle. The schedulers arbitrate for the dispatch ports to schedule uops for execution.

Register files 208, 210 may be arranged between schedulers 202, 204, 206, and execution units 212, 214, 216, 218, 220, 222, 224 in execution block 211. Each of register files 208, 210 perform integer and floating point operations, respectively. Each register file 208, 210, may include a bypass network that may bypass or forward just completed results that have not yet been written into the register file to new dependent uops. Integer register file 208 and floating point register file 210 may communicate data with the other. In one embodiment, integer register file 208 may be split into two separate register files, one register file for low-order thirty-two bits of data and a second register file for high order thirty-two bits of data. Floating point register file 210 may include 128-bit wide entries because floating point instructions typically have operands from 64 to 128 bits in width.

Execution block 211 may contain execution units 212, 214, 216, 218, 220, 222, 224. Execution units 212, 214, 216, 218, 220, 222, 224 may execute the instructions. Execution block 211 may include register files 208, 210 that store the integer and floating point data operand values that the micro-instructions need to execute. In one embodiment, processor 200 may comprise a number of execution units: address generation unit (AGU) 212, AGU 214, fast ALU 216, fast ALU 218, slow ALU 220, floating point ALU 222, floating point move unit 224. In another embodiment, floating point execution blocks 222, 224, may execute floating point, MMX, SIMD, and SSE, or other operations. In yet another embodiment, floating point ALU 222 may include a 64-bit by 64-bit floating point divider to execute divide, square root, and remainder micro-ops. In various embodiments, instructions involving a floating point value may be handled with the floating point hardware. In one embodiment, ALU operations may be passed to high-speed ALU execution units 216, 218. High-speed ALUs 216, 218 may execute fast operations with an effective latency of half a clock cycle. In one embodiment, most complex integer operations go to slow ALU 220 as slow ALU 220 may include integer execution hardware for long-latency type of operations, such as a multiplier, shifts, flag logic, and branch processing. Memory load/store operations may be executed by AGUs 212, 214. In one embodiment, integer ALUs 216, 218, 220 may perform integer operations on 64-bit data operands. In other embodiments, ALUs 216, 218, 220 may be implemented to support a variety of data bit sizes including sixteen, thirty-two, 128, 256, etc. Similarly, floating point units 222, 224 may be implemented to support a range of operands having bits of various widths. In one embodiment, floating point units 222, 224, may operate on 128-bit wide packed data operands in conjunction with SIMD and multimedia instructions.

In one embodiment, uops schedulers 202, 204, 206, dispatch dependent operations before the parent load has finished executing. As uops may be speculatively scheduled and executed in processor 200, processor 200 may also include circuits with logic to handle memory misses. If a data load misses in the data cache, there may be dependent operations in flight in the pipeline that have left the scheduler with temporarily incorrect data. A replay mechanism tracks and re-executes instructions that use incorrect data. Only the dependent operations might need to be replayed and the independent ones may be allowed to complete. The schedulers and replay mechanism of one embodiment of a processor may also be designed to catch instruction sequences for text string comparison operations.

The term “registers” may refer to the on-board processor storage locations that may be used as part of instructions to identify operands. In other words, registers may be those that may be usable from the outside of the processor (from a programmer's perspective). However, in some embodiments registers might not be limited to a particular type of circuit. Rather, a register may store data, provide data, and perform the functions described herein. The registers described herein may be implemented by circuitry within a processor using any number of different techniques, such as dedicated physical registers, dynamically allocated physical registers using register renaming, combinations of dedicated and dynamically allocated physical registers, etc. In one embodiment, integer registers store 32-bit integer data. A register file of one embodiment also contains eight multimedia SIMD registers for packed data. For the discussions below, the registers may be understood to be data registers designed to hold packed data, such as 64-bit wide MMX™ registers (also referred to as ‘mm’ registers in some instances) in microprocessors enabled with MMX technology from Intel Corporation of Santa Clara, Calif. These MMX registers, available in both integer and floating point forms, may operate with packed data elements that accompany SIMD and SSE instructions. Similarly, 128-bit wide XMM registers relating to SSE2, SSE3, SSE4, or beyond (referred to generically as “SSEx”) technology may hold such packed data operands. In one embodiment, in storing packed data and integer data, the registers do not need to differentiate between the two data types. In one embodiment, integer and floating point may be contained in the same register file or different register files. Furthermore, in one embodiment, floating point and integer data may be stored in different registers or the same registers.

In the examples of the following figures, a number of data operands may be described. FIG. 3A illustrates various packed data type representations in multimedia registers, in accordance with embodiments of the present disclosure. FIG. 3A illustrates data types for a packed byte 310, a packed word 320, and a packed doubleword (dword) 330 for 128-bit wide operands. Packed byte format 310 of this example may be 128 bits long and contains sixteen packed byte data elements. A byte may be defined, for example, as eight bits of data. Information for each byte data element may be stored in bit 7 through bit 0 for byte 0, bit 15 through bit 8 for byte 1, bit 23 through bit 16 for byte 2, and finally bit 120 through bit 127 for byte 15. Thus, all available bits may be used in the register. This storage arrangement increases the storage efficiency of the processor. As well, with sixteen data elements accessed, one operation may now be performed on sixteen data elements in parallel.

Generally, a data element may include an individual piece of data that is stored in a single register or memory location with other data elements of the same length. In packed data sequences relating to SSEx technology, the number of data elements stored in a XMM register may be 128 bits divided by the length in bits of an individual data element. Similarly, in packed data sequences relating to MMX and SSE technology, the number of data elements stored in an MMX register may be 64 bits divided by the length in bits of an individual data element. Although the data types illustrated in FIG. 3A may be 128 bits long, embodiments of the present disclosure may also operate with 64-bit wide or other sized operands. Packed word format 320 of this example may be 128 bits long and contains eight packed word data elements. Each packed word contains sixteen bits of information. Packed doubleword format 330 of FIG. 3A may be 128 bits long and contains four packed doubleword data elements. Each packed doubleword data element contains thirty-two bits of information. A packed quadword may be 128 bits long and contain two packed quad-word data elements.

FIG. 3B illustrates possible in-register data storage formats, in accordance with embodiments of the present disclosure. Each packed data may include more than one independent data element. Three packed data formats are illustrated; packed half 341, packed single 342, and packed double 343. One embodiment of packed half 341, packed single 342, and packed double 343 contain fixed-point data elements. For another embodiment one or more of packed half 341, packed single 342, and packed double 343 may contain floating-point data elements. One embodiment of packed half 341 may be 128 bits long containing eight 16-bit data elements. One embodiment of packed single 342 may be 128 bits long and contains four 32-bit data elements. One embodiment of packed double 343 may be 128 bits long and contains two 64-bit data elements. It will be appreciated that such packed data formats may be further extended to other register lengths, for example, to 96-bits, 160-bits, 192-bits, 224-bits, 256-bits, 512-bits or more.

FIG. 3C illustrates various signed and unsigned packed data type representations in multimedia registers, in accordance with embodiments of the present disclosure. Unsigned packed byte representation 344 illustrates the storage of an unsigned packed byte in a SIMD register. Information for each byte data element may be stored in bit 7 through bit 0 for byte 0, bit 15 through bit 8 for byte 1, bit 23 through bit 16 for byte 2, and finally bit 120 through bit 127 for byte 15. Thus, all available bits may be used in the register. This storage arrangement may increase the storage efficiency of the processor. As well, with sixteen data elements accessed, one operation may now be performed on sixteen data elements in a parallel fashion. Signed packed byte representation 345 illustrates the storage of a signed packed byte. Note that the eighth bit of every byte data element may be the sign indicator. Unsigned packed word representation 346 illustrates how word seven through word zero may be stored in a SIMD register. Signed packed word representation 347 may be similar to the unsigned packed word in-register representation 346. Note that the sixteenth bit of each word data element may be the sign indicator. Unsigned packed doubleword representation 348 shows how doubleword data elements are stored. Signed packed doubleword representation 349 may be similar to unsigned packed doubleword in-register representation 348. Note that the necessary sign bit may be the thirty-second bit of each doubleword data element.

FIG. 3D illustrates an embodiment of an operation encoding (opcode). Furthermore, format 360 may include register/memory operand addressing modes corresponding with a type of opcode format described in the “IA-32 Intel Architecture Software Developer's Manual Volume 2: Instruction Set Reference,” which is available from Intel Corporation, Santa Clara, Calif. on the world-wide-web (www) at intel.com/design/litcentr. In one embodiment, an instruction may be encoded by one or more of fields 361 and 362. Up to two operand locations per instruction may be identified, including up to two source operand identifiers 364 and 365. In one embodiment, destination operand identifier 366 may be the same as source operand identifier 364, whereas in other embodiments they may be different. In another embodiment, destination operand identifier 366 may be the same as source operand identifier 365, whereas in other embodiments they may be different. In one embodiment, one of the source operands identified by source operand identifiers 364 and 365 may be overwritten by the results of the text string comparison operations, whereas in other embodiments identifier 364 corresponds to a source register element and identifier 365 corresponds to a destination register element. In one embodiment, operand identifiers 364 and 365 may identify 32-bit or 64-bit source and destination operands.

FIG. 3E illustrates another possible operation encoding (opcode) format 370, having forty or more bits, in accordance with embodiments of the present disclosure. Opcode format 370 corresponds with opcode format 360 and comprises an optional prefix byte 378. An instruction according to one embodiment may be encoded by one or more of fields 378, 371, and 372. Up to two operand locations per instruction may be identified by source operand identifiers 374 and 375 and by prefix byte 378. In one embodiment, prefix byte 378 may be used to identify 32-bit or 64-bit source and destination operands. In one embodiment, destination operand identifier 376 may be the same as source operand identifier 374, whereas in other embodiments they may be different. For another embodiment, destination operand identifier 376 may be the same as source operand identifier 375, whereas in other embodiments they may be different. In one embodiment, an instruction operates on one or more of the operands identified by operand identifiers 374 and 375 and one or more operands identified by operand identifiers 374 and 375 may be overwritten by the results of the instruction, whereas in other embodiments, operands identified by identifiers 374 and 375 may be written to another data element in another register. Opcode formats 360 and 370 allow register to register, memory to register, register by memory, register by register, register by immediate, register to memory addressing specified in part by MOD fields 363 and 373 and by optional scale-index-base and displacement bytes.

FIG. 3F illustrates yet another possible operation encoding (opcode) format, in accordance with embodiments of the present disclosure. 64-bit single instruction multiple data (SIMD) arithmetic operations may be performed through a coprocessor data processing (CDP) instruction. Operation encoding (opcode) format 380 depicts one such CDP instruction having CDP opcode fields 382 and 389. The type of CDP instruction, for another embodiment, operations may be encoded by one or more of fields 383, 384, 387, and 388. Up to three operand locations per instruction may be identified, including up to two source operand identifiers 385 and 390 and one destination operand identifier 386. One embodiment of the coprocessor may operate on eight, sixteen, thirty-two, and 64-bit values. In one embodiment, an instruction may be performed on integer data elements. In some embodiments, an instruction may be executed conditionally, using condition field 381. For some embodiments, source data sizes may be encoded by field 383. In some embodiments, Zero (Z), negative (N), carry (C), and overflow (V) detection may be done on SIMD fields. For some instructions, the type of saturation may be encoded by field 384.

FIG. 4A is a block diagram illustrating an in-order pipeline and a register renaming stage, out-of-order issue/execution pipeline, in accordance with embodiments of the present disclosure. FIG. 4B is a block diagram illustrating an in-order architecture core and circuitry for register renaming, circuitry for out-of-order issue/execution to be included in a processor, in accordance with embodiments of the present disclosure. The solid lined boxes in FIG. 4A illustrate the in-order pipeline, while the dashed lined boxes illustrates the register renaming, out-of-order issue/execution pipeline. Similarly, the solid lined boxes in FIG. 4B illustrate the in-order architecture logic, while the dashed lined boxes illustrates the register renaming logic and out-of-order issue/execution logic.

In FIG. 4A, a processor pipeline 400 may include a fetch stage 402, a length decode stage 404, a decode stage 406, an allocation stage 408, a renaming stage 410, a scheduling (also known as a dispatch or issue) stage 412, a register read/memory read stage 414, an execute stage 416, a write-back/memory-write stage 418, an exception handling stage 422, and a commit stage 424.

In FIG. 4B, arrows denote a coupling between two or more units and the direction of the arrow indicates a direction of data flow between those units. FIG. 4B shows processor core 490 including a front end unit 430 coupled to an execution engine unit 450, and both may be coupled to a memory unit 470.

Core 490 may be a reduced instruction set computing (RISC) core, a complex instruction set computing (CISC) core, a very long instruction word (VLIW) core, or a hybrid or alternative core type. In one embodiment, core 490 may be a special-purpose core, such as, for example, a network or communication core, compression engine, graphics core, or the like.

Front end unit 430 may include a branch prediction unit 432 coupled to an instruction cache unit 434. Instruction cache unit 434 may be coupled to an instruction translation lookaside buffer (TLB) 436. TLB 436 may be coupled to an instruction fetch unit 438, which is coupled to a decode unit 440. Decode unit 440 may decode instructions, and generate as an output one or more micro-operations, micro-code entry points, microinstructions, other instructions, or other control signals, which may be decoded from, or which otherwise reflect, or may be derived from, the original instructions. The decoder may be implemented using various different mechanisms. Examples of suitable mechanisms include, but are not limited to, look-up tables, hardware implementations, programmable logic arrays (PLAs), microcode read-only memories (ROMs), etc. In one embodiment, instruction cache unit 434 may be further coupled to a level 2 (L2) cache unit 476 in memory unit 470. Decode unit 440 may be coupled to a rename/allocator unit 452 in execution engine unit 450.

Execution engine unit 450 may include rename/allocator unit 452 coupled to a retirement unit 454 and a set of one or more scheduler units 456. Scheduler units 456 represent any number of different schedulers, including reservations stations, central instruction window, etc. Scheduler units 456 may be coupled to physical register file units 458. Each of physical register file units 458 represents one or more physical register files, different ones of which store one or more different data types, such as scalar integer, scalar floating point, packed integer, packed floating point, vector integer, vector floating point, etc., status (e.g., an instruction pointer that is the address of the next instruction to be executed), etc. Physical register file units 458 may be overlapped by retirement unit 154 to illustrate various ways in which register renaming and out-of-order execution may be implemented (e.g., using one or more reorder buffers and one or more retirement register files, using one or more future files, one or more history buffers, and one or more retirement register files; using register maps and a pool of registers; etc.). Generally, the architectural registers may be visible from the outside of the processor or from a programmer's perspective. The registers might not be limited to any known particular type of circuit. Various different types of registers may be suitable as long as they store and provide data as described herein. Examples of suitable registers include, but might not be limited to, dedicated physical registers, dynamically allocated physical registers using register renaming, combinations of dedicated and dynamically allocated physical registers, etc. Retirement unit 454 and physical register file units 458 may be coupled to execution clusters 460. Execution clusters 460 may include a set of one or more execution units 162 and a set of one or more memory access units 464. Execution units 462 may perform various operations (e.g., shifts, addition, subtraction, multiplication) and on various types of data (e.g., scalar floating point, packed integer, packed floating point, vector integer, vector floating point). While some embodiments may include a number of execution units dedicated to specific functions or sets of functions, other embodiments may include only one execution unit or multiple execution units that all perform all functions. Scheduler units 456, physical register file units 458, and execution clusters 460 are shown as being possibly plural because certain embodiments create separate pipelines for certain types of data/operations (e.g., a scalar integer pipeline, a scalar floating point/packed integer/packed floating point/vector integer/vector floating point pipeline, and/or a memory access pipeline that each have their own scheduler unit, physical register file unit, and/or execution cluster—and in the case of a separate memory access pipeline, certain embodiments may be implemented in which only the execution cluster of this pipeline has memory access units 464). It should also be understood that where separate pipelines are used, one or more of these pipelines may be out-of-order issue/execution and the rest in-order.

The set of memory access units 464 may be coupled to memory unit 470, which may include a data TLB unit 472 coupled to a data cache unit 474 coupled to a level 2 (L2) cache unit 476. In one exemplary embodiment, memory access units 464 may include a load unit, a store address unit, and a store data unit, each of which may be coupled to data TLB unit 472 in memory unit 470. L2 cache unit 476 may be coupled to one or more other levels of cache and eventually to a main memory.

By way of example, the exemplary register renaming, out-of-order issue/execution core architecture may implement pipeline 400 as follows: 1) instruction fetch 438 may perform fetch and length decoding stages 402 and 404; 2) decode unit 440 may perform decode stage 406; 3) rename/allocator unit 452 may perform allocation stage 408 and renaming stage 410; 4) scheduler units 456 may perform schedule stage 412; 5) physical register file units 458 and memory unit 470 may perform register read/memory read stage 414; execution cluster 460 may perform execute stage 416; 6) memory unit 470 and physical register file units 458 may perform write-back/memory-write stage 418; 7) various units may be involved in the performance of exception handling stage 422; and 8) retirement unit 454 and physical register file units 458 may perform commit stage 424.

Core 490 may support one or more instructions sets (e.g., the x86 instruction set (with some extensions that have been added with newer versions); the MIPS instruction set of MIPS Technologies of Sunnyvale, Calif.; the ARM instruction set (with optional additional extensions such as NEON) of ARM Holdings of Sunnyvale, Calif.).

It should be understood that the core may support multithreading (executing two or more parallel sets of operations or threads) in a variety of manners. Multithreading support may be performed by, for example, including time sliced multithreading, simultaneous multithreading (where a single physical core provides a logical core for each of the threads that physical core is simultaneously multithreading), or a combination thereof. Such a combination may include, for example, time sliced fetching and decoding and simultaneous multithreading thereafter such as in the Intel® Hyperthreading technology.

While register renaming may be described in the context of out-of-order execution, it should be understood that register renaming may be used in an in-order architecture. While the illustrated embodiment of the processor may also include a separate instruction and data cache units 434/474 and a shared L2 cache unit 476, other embodiments may have a single internal cache for both instructions and data, such as, for example, a Level 1 (L1) internal cache, or multiple levels of internal cache. In some embodiments, the system may include a combination of an internal cache and an external cache that may be external to the core and/or the processor. In other embodiments, all of the cache may be external to the core and/or the processor.

FIG. 5A is a block diagram of a processor 500, in accordance with embodiments of the present disclosure. In one embodiment, processor 500 may include a multicore processor. Processor 500 may include a system agent 510 communicatively coupled to one or more cores 502. Furthermore, cores 502 and system agent 510 may be communicatively coupled to one or more caches 506. Cores 502, system agent 510, and caches 506 may be communicatively coupled via one or more memory control units 552. Furthermore, cores 502, system agent 510, and caches 506 may be communicatively coupled to a graphics module 560 via memory control units 552.

Processor 500 may include any suitable mechanism for interconnecting cores 502, system agent 510, and caches 506, and graphics module 560. In one embodiment, processor 500 may include a ring-based interconnect unit 508 to interconnect cores 502, system agent 510, and caches 506, and graphics module 560. In other embodiments, processor 500 may include any number of well-known techniques for interconnecting such units. Ring-based interconnect unit 508 may utilize memory control units 552 to facilitate interconnections.

Processor 500 may include a memory hierarchy comprising one or more levels of caches within the cores, one or more shared cache units such as caches 506, or external memory (not shown) coupled to the set of integrated memory controller units 552. Caches 506 may include any suitable cache. In one embodiment, caches 506 may include one or more mid-level caches, such as level 2 (L2), level 3 (L3), level 4 (L4), or other levels of cache, a last level cache (LLC), and/or combinations thereof.

In various embodiments, one or more of cores 502 may perform multi-threading. System agent 510 may include components for coordinating and operating cores 502. System agent unit 510 may include for example a power control unit (PCU). The PCU may be or include logic and components needed for regulating the power state of cores 502. System agent 510 may include a display engine 512 for driving one or more externally connected displays or graphics module 560. System agent 510 may include an interface for communications busses for graphics. In one embodiment, the interface may be implemented by PCI Express (PCIe). In a further embodiment, the interface may be implemented by PCI Express Graphics (PEG) 514. System agent 510 may include a direct media interface (DMI) 516. DMI 516 may provide links between different bridges on a motherboard or other portion of a computer system. System agent 510 may include a PCIe bridge 518 for providing PCIe links to other elements of a computing system. PCIe bridge 518 may be implemented using a memory controller 520 and coherence logic 522.

Cores 502 may be implemented in any suitable manner. Cores 502 may be homogenous or heterogeneous in terms of architecture and/or instruction set. In one embodiment, some of cores 502 may be in-order while others may be out-of-order. In another embodiment, two or more of cores 502 may execute the same instruction set, while others may execute only a subset of that instruction set or a different instruction set.

Processor 500 may include a general-purpose processor, such as a Core™ i3, i5, i7, 2 Duo and Quad, Xeon™, Itanium™, XScale™ or StrongARM™ processor, which may be available from Intel Corporation, of Santa Clara, Calif. Processor 500 may be provided from another company, such as ARM Holdings, Ltd, MIPS, etc. Processor 500 may be a special-purpose processor, such as, for example, a network or communication processor, compression engine, graphics processor, co-processor, embedded processor, or the like. Processor 500 may be implemented on one or more chips. Processor 500 may be a part of and/or may be implemented on one or more substrates using any of a number of process technologies, such as, for example, BiCMOS, CMOS, or NMOS.

In one embodiment, a given one of caches 506 may be shared by multiple ones of cores 502. In another embodiment, a given one of caches 506 may be dedicated to one of cores 502. The assignment of caches 506 to cores 502 may be handled by a cache controller or other suitable mechanism. A given one of caches 506 may be shared by two or more cores 502 by implementing time-slices of a given cache 506.

Graphics module 560 may implement an integrated graphics processing subsystem. In one embodiment, graphics module 560 may include a graphics processor. Furthermore, graphics module 560 may include a media engine 565. Media engine 565 may provide media encoding and video decoding.

FIG. 5B is a block diagram of an example implementation of a core 502, in accordance with embodiments of the present disclosure. Core 502 may include a front end 570 communicatively coupled to an out-of-order engine 580. Core 502 may be communicatively coupled to other portions of processor 500 through cache hierarchy 503.

Front end 570 may be implemented in any suitable manner, such as fully or in part by front end 201 as described above. In one embodiment, front end 570 may communicate with other portions of processor 500 through cache hierarchy 503. In a further embodiment, front end 570 may fetch instructions from portions of processor 500 and prepare the instructions to be used later in the processor pipeline as they are passed to out-of-order execution engine 580.

Out-of-order execution engine 580 may be implemented in any suitable manner, such as fully or in part by out-of-order execution engine 203 as described above. Out-of-order execution engine 580 may prepare instructions received from front end 570 for execution. Out-of-order execution engine 580 may include an allocate module 1282. In one embodiment, allocate module 1282 may allocate resources of processor 500 or other resources, such as registers or buffers, to execute a given instruction. Allocate module 1282 may make allocations in schedulers, such as a memory scheduler, fast scheduler, or floating point scheduler. Such schedulers may be represented in FIG. 5B by resource schedulers 584. Allocate module 1282 may be implemented fully or in part by the allocation logic described in conjunction with FIG. 2. Resource schedulers 584 may determine when an instruction is ready to execute based on the readiness of a given resource's sources and the availability of execution resources needed to execute an instruction. Resource schedulers 584 may be implemented by, for example, schedulers 202, 204, 206 as discussed above. Resource schedulers 584 may schedule the execution of instructions upon one or more resources. In one embodiment, such resources may be internal to core 502, and may be illustrated, for example, as resources 586. In another embodiment, such resources may be external to core 502 and may be accessible by, for example, cache hierarchy 503. Resources may include, for example, memory, caches, register files, or registers. Resources internal to core 502 may be represented by resources 586 in FIG. 5B. As necessary, values written to or read from resources 586 may be coordinated with other portions of processor 500 through, for example, cache hierarchy 503. As instructions are assigned resources, they may be placed into a reorder buffer 588. Reorder buffer 588 may track instructions as they are executed and may selectively reorder their execution based upon any suitable criteria of processor 500. In one embodiment, reorder buffer 588 may identify instructions or a series of instructions that may be executed independently. Such instructions or a series of instructions may be executed in parallel from other such instructions. Parallel execution in core 502 may be performed by any suitable number of separate execution blocks or virtual processors. In one embodiment, shared resources—such as memory, registers, and caches—may be accessible to multiple virtual processors within a given core 502. In other embodiments, shared resources may be accessible to multiple processing entities within processor 500.

Cache hierarchy 503 may be implemented in any suitable manner. For example, cache hierarchy 503 may include one or more lower or mid-level caches, such as caches 572, 574 through logic block 576. In one embodiment, cache hierarchy 503 may include an LLC 595 communicatively coupled to caches 572, 574. In another embodiment, LLC 595 may be implemented in a module 590 accessible to all processing entities of processor 500. In a further embodiment, module 590 may be implemented in an uncore module of processors from Intel, Inc. Module 590 may include portions or subsystems of processor 500 necessary for the execution of core 502 but might not be implemented within core 502. Besides LLC 595, Module 590 may include, for example, hardware interfaces, memory coherency coordinators, interprocessor interconnects, instruction pipelines, or memory controllers. Access to RAM 599 available to processor 500 may be made through module 590 and, more specifically, LLC 595. Furthermore, other instances of core 502 may similarly access module 590. Coordination of the instances of core 502 may be facilitated in part through module 590.

FIGS. 6-8 may illustrate exemplary systems suitable for including processor 500, while FIG. 9 may illustrate an exemplary system on a chip (SoC) that may include one or more of cores 502. Other system designs and implementations known in the arts for laptops, desktops, handheld PCs, personal digital assistants, engineering workstations, servers, network devices, network hubs, switches, embedded processors, digital signal processors (DSPs), graphics devices, video game devices, set-top boxes, micro controllers, cell phones, portable media players, hand held devices, and various other electronic devices, may also be suitable. In general, a huge variety of systems or electronic devices that incorporate a processor and/or other execution logic as disclosed herein may be generally suitable.

FIG. 6 illustrates a block diagram of a system 600, in accordance with embodiments of the present disclosure. System 600 may include one or more processors 610, 615, which may be coupled to graphics memory controller hub (GMCH) 620. The optional nature of additional processors 615 is denoted in FIG. 6 with broken lines.

Each processor 610,615 may be some version of processor 500. However, it should be noted that integrated graphics logic and integrated memory control units might not exist in processors 610,615. FIG. 6 illustrates that GMCH 620 may be coupled to a memory 640 that may be, for example, a dynamic random access memory (DRAM). The DRAM may, for at least one embodiment, be associated with a non-volatile cache.

GMCH 620 may be a chipset, or a portion of a chipset. GMCH 620 may communicate with processors 610, 615 and control interaction between processors 610, 615 and memory 640. GMCH 620 may also act as an accelerated bus interface between the processors 610, 615 and other elements of system 600. In one embodiment, GMCH 620 communicates with processors 610, 615 via a multi-drop bus, such as a frontside bus (FSB) 695.

Furthermore, GMCH 620 may be coupled to a display 645 (such as a flat panel display). In one embodiment, GMCH 620 may include an integrated graphics accelerator. GMCH 620 may be further coupled to an input/output (I/O) controller hub (ICH) 650, which may be used to couple various peripheral devices to system 600. External graphics device 660 may include be a discrete graphics device coupled to ICH 650 along with another peripheral device 670.

In other embodiments, additional or different processors may also be present in system 600. For example, additional processors 610, 615 may include additional processors that may be the same as processor 610, additional processors that may be heterogeneous or asymmetric to processor 610, accelerators (such as, e.g., graphics accelerators or digital signal processing (DSP) units), field programmable gate arrays, or any other processor. There may be a variety of differences between the physical resources 610, 615 in terms of a spectrum of metrics of merit including architectural, micro-architectural, thermal, power consumption characteristics, and the like. These differences may effectively manifest themselves as asymmetry and heterogeneity amongst processors 610, 615. For at least one embodiment, various processors 610, 615 may reside in the same die package.

FIG. 7 illustrates a block diagram of a second system 700, in accordance with embodiments of the present disclosure. As shown in FIG. 7, multiprocessor system 700 may include a point-to-point interconnect system, and may include a first processor 770 and a second processor 780 coupled via a point-to-point interconnect 750. Each of processors 770 and 780 may be some version of processor 500 as one or more of processors 610,615.

While FIG. 7 may illustrate two processors 770, 780, it is to be understood that the scope of the present disclosure is not so limited. In other embodiments, one or more additional processors may be present in a given processor.

Processors 770 and 780 are shown including integrated memory controller units 772 and 782, respectively. Processor 770 may also include as part of its bus controller units point-to-point (P-P) interfaces 776 and 778; similarly, second processor 780 may include P-P interfaces 786 and 788. Processors 770, 780 may exchange information via a point-to-point (P-P) interface 750 using P-P interface circuits 778, 788. As shown in FIG. 7, IMCs 772 and 782 may couple the processors to respective memories, namely a memory 732 and a memory 734, which in one embodiment may be portions of main memory locally attached to the respective processors.

Processors 770, 780 may each exchange information with a chipset 790 via individual P-P interfaces 752, 754 using point to point interface circuits 776, 794, 786, 798. In one embodiment, chipset 790 may also exchange information with a high-performance graphics circuit 738 via interface 792 over a high-performance graphics bus 739.

A shared cache (not shown) may be included in either processor or outside of both processors, yet connected with the processors via P-P interconnect, such that either or both processors' local cache information may be stored in the shared cache if a processor is placed into a low power mode.

Chipset 790 may be coupled to a first bus 716 via an interface 796. In one embodiment, first bus 716 may be a Peripheral Component Interconnect (PCI) bus, or a bus such as a PCI Express bus or another third generation I/O interconnect bus, although the scope of the present disclosure is not so limited.

As shown in FIG. 7, various I/O devices 714 may be coupled to first bus 716, along with a bus bridge 718 which couples first bus 716 to a second bus 720. In one embodiment, second bus 720 may be a low pin count (LPC) bus. Various devices may be coupled to second bus 720 including, for example, a keyboard and/or mouse 722, communication devices 727 and a storage unit 728 such as a disk drive or other mass storage device which may include instructions/code and data 730, in one embodiment. Further, an audio I/O 724 may be coupled to second bus 720. Note that other architectures may be possible. For example, instead of the point-to-point architecture of FIG. 7, a system may implement a multi-drop bus or other such architecture.

FIG. 8 illustrates a block diagram of a third system 800 in accordance with embodiments of the present disclosure. Like elements in FIGS. 7 and 8 bear like reference numerals, and certain aspects of FIG. 7 have been omitted from FIG. 8 in order to avoid obscuring other aspects of FIG. 8.

FIG. 8 illustrates that processors 870, 880 may include integrated memory and I/O control logic (“CL”) 872 and 882, respectively. For at least one embodiment, CL 872, 882 may include integrated memory controller units such as that described above in connection with FIGS. 5 and 7. In addition, CL 872, 882 may also include I/O control logic. FIG. 8 illustrates that not only memories 832, 834 may be coupled to CL 872, 882, but also that I/O devices 814 may also be coupled to control logic 872, 882. Legacy I/O devices 815 may be coupled to chipset 890.

FIG. 9 illustrates a block diagram of a SoC 900, in accordance with embodiments of the present disclosure. Similar elements in FIG. 5 bear like reference numerals. Also, dashed lined boxes may represent optional features on more advanced SoCs. An interconnect units 902 may be coupled to: an application processor 910 which may include a set of one or more cores 502A-N, including respective local caches 504A-N, and shared cache units 506; a system agent unit 510; a bus controller units 916; an integrated memory controller units 914; a set or one or more media processors 920 which may include integrated graphics logic 908, an image processor 924 for providing still and/or video camera functionality, an audio processor 926 for providing hardware audio acceleration, and a video processor 928 for providing video encode/decode acceleration; an static random access memory (SRAM) unit 930; a direct memory access (DMA) unit 932; and a display unit 940 for coupling to one or more external displays.

FIG. 10 illustrates a processor containing a central processing unit (CPU) and a graphics processing unit (GPU), which may perform at least one instruction, in accordance with embodiments of the present disclosure. In one embodiment, an instruction to perform operations according to at least one embodiment could be performed by the CPU. In another embodiment, the instruction could be performed by the GPU. In still another embodiment, the instruction may be performed through a combination of operations performed by the GPU and the CPU. For example, in one embodiment, an instruction in accordance with one embodiment may be received and decoded for execution on the GPU. However, one or more operations within the decoded instruction may be performed by a CPU and the result returned to the GPU for final retirement of the instruction. Conversely, in some embodiments, the CPU may act as the primary processor and the GPU as the co-processor.

In some embodiments, instructions that benefit from highly parallel, throughput processors may be performed by the GPU, while instructions that benefit from the performance of processors that benefit from deeply pipelined architectures may be performed by the CPU. For example, graphics, scientific applications, financial applications and other parallel workloads may benefit from the performance of the GPU and be executed accordingly, whereas more sequential applications, such as operating system kernel or application code may be better suited for the CPU.

In FIG. 10, processor 1000 includes a CPU 1005, GPU 1010, image processor 1015, video processor 1020, USB controller 1025, UART controller 1030, SPI/SDIO controller 1035, display device 1040, memory interface controller 1045, MIPI controller 1050, flash memory controller 1055, dual data rate (DDR) controller 1060, security engine 1065, and I²S/I²C controller 1070. Other logic and circuits may be included in the processor of FIG. 10, including more CPUs or GPUs and other peripheral interface controllers.

One or more aspects of at least one embodiment may be implemented by representative data stored on a machine-readable medium which represents various logic within the processor, which when read by a machine causes the machine to fabricate logic to perform the techniques described herein. Such representations, known as “IP cores” may be stored on a tangible, machine-readable medium (“tape”) and supplied to various customers or manufacturing facilities to load into the fabrication machines that actually make the logic or processor. For example, IP cores, such as the Cortex™ family of processors developed by ARM Holdings, Ltd. and Loongson IP cores developed the Institute of Computing Technology (ICT) of the Chinese Academy of Sciences may be licensed or sold to various customers or licensees, such as Texas Instruments, Qualcomm, Apple, or Samsung and implemented in processors produced by these customers or licensees.

FIG. 11 illustrates a block diagram illustrating the development of IP cores, in accordance with embodiments of the present disclosure. Storage 1130 may include simulation software 1120 and/or hardware or software model 1110. In one embodiment, the data representing the IP core design may be provided to storage 1130 via memory 1140 (e.g., hard disk), wired connection (e.g., internet) 1150 or wireless connection 1160. The IP core information generated by the simulation tool and model may then be transmitted to a fabrication facility where it may be fabricated by a 3^(rd) party to perform at least one instruction in accordance with at least one embodiment.

In some embodiments, one or more instructions may correspond to a first type or architecture (e.g., x86) and be translated or emulated on a processor of a different type or architecture (e.g., ARM). An instruction, according to one embodiment, may therefore be performed on any processor or processor type, including ARM, x86, MIPS, a GPU, or other processor type or architecture.

FIG. 12 illustrates how an instruction of a first type may be emulated by a processor of a different type, in accordance with embodiments of the present disclosure. In FIG. 12, program 1205 contains some instructions that may perform the same or substantially the same function as an instruction according to one embodiment. However the instructions of program 1205 may be of a type and/or format that is different from or incompatible with processor 1215, meaning the instructions of the type in program 1205 may not be able to execute natively by the processor 1215. However, with the help of emulation logic, 1210, the instructions of program 1205 may be translated into instructions that may be natively be executed by the processor 1215. In one embodiment, the emulation logic may be embodied in hardware. In another embodiment, the emulation logic may be embodied in a tangible, machine-readable medium containing software to translate instructions of the type in program 1205 into the type natively executable by processor 1215. In other embodiments, emulation logic may be a combination of fixed-function or programmable hardware and a program stored on a tangible, machine-readable medium. In one embodiment, the processor contains the emulation logic, whereas in other embodiments, the emulation logic exists outside of the processor and may be provided by a third party. In one embodiment, the processor may load the emulation logic embodied in a tangible, machine-readable medium containing software by executing microcode or firmware contained in or associated with the processor.

FIG. 13 illustrates a block diagram contrasting the use of a software instruction converter to convert binary instructions in a source instruction set to binary instructions in a target instruction set, in accordance with embodiments of the present disclosure. In the illustrated embodiment, the instruction converter may be a software instruction converter, although the instruction converter may be implemented in software, firmware, hardware, or various combinations thereof. FIG. 13 shows a program in a high level language 1302 may be compiled using an x86 compiler 1304 to generate x86 binary code 1306 that may be natively executed by a processor with at least one x86 instruction set core 1316. The processor with at least one x86 instruction set core 1316 represents any processor that may perform substantially the same functions as an Intel processor with at least one x86 instruction set core by compatibly executing or otherwise processing (1) a substantial portion of the instruction set of the Intel x86 instruction set core or (2) object code versions of applications or other software targeted to run on an Intel processor with at least one x86 instruction set core, in order to achieve substantially the same result as an Intel processor with at least one x86 instruction set core. x86 compiler 1304 represents a compiler that may be operable to generate x86 binary code 1306 (e.g., object code) that may, with or without additional linkage processing, be executed on the processor with at least one x86 instruction set core 1316. Similarly, FIG. 13 shows the program in high level language 1302 may be compiled using an alternative instruction set compiler 1308 to generate alternative instruction set binary code 1310 that may be natively executed by a processor without at least one x86 instruction set core 1314 (e.g., a processor with cores that execute the MIPS instruction set of MIPS Technologies of Sunnyvale, Calif. and/or that execute the ARM instruction set of ARM Holdings of Sunnyvale, Calif.). Instruction converter 1312 may be used to convert x86 binary code 1306 into code that may be natively executed by the processor without an x86 instruction set core 1314. This converted code might not be the same as alternative instruction set binary code 1310; however, the converted code will accomplish the general operation and be made up of instructions from the alternative instruction set. Thus, instruction converter 1312 represents software, firmware, hardware, or a combination thereof that, through emulation, simulation or any other process, allows a processor or other electronic device that does not have an x86 instruction set processor or core to execute x86 binary code 1306.

FIG. 14 is a block diagram of an instruction set architecture 1400 of a processor, in accordance with embodiments of the present disclosure. Instruction set architecture 1400 may include any suitable number or kind of components.

For example, instruction set architecture 1400 may include processing entities such as one or more cores 1406, 1407 within a processor subsystem 1405 and a graphics processing unit 1415. Cores 1406, 1407 may be communicatively coupled to the rest of instruction set architecture 1400 through any suitable mechanism, such as through a bus or cache. In one embodiment, cores 1406, 1407 may be communicatively coupled through an L2 cache control 1408, which may include a bus interface unit 1409 and an L2 cache 1411. Cores 1406, 1407 and graphics processing unit 1415 may be communicatively coupled to each other and to the remainder of instruction set architecture 1400 through interconnect 1410. In one embodiment, graphics processing unit 1415 may use a video code 1420 defining the manner in which particular video signals will be encoded and decoded for output.

Instruction set architecture 1400 may also include any number or kind of interfaces, controllers, or other mechanisms for interfacing or communicating with other portions of an electronic device or system. Such mechanisms may facilitate interaction with, for example, peripherals, communications devices, other processors, or memory. In the example of FIG. 14, instruction set architecture 1400 may include a liquid crystal display (LCD) video interface 1425, a subscriber interface module (SIM) interface 1430, a boot ROM interface 1435, a synchronous dynamic random access memory (SDRAM) controller 1440, a flash controller 1445, and a serial peripheral interface (SPI) master unit 1450. LCD video interface 1425 may provide output of video signals from, for example, GPU 1415 and through, for example, a mobile industry processor interface (MIPI) 1490 or a high-definition multimedia interface (HDMI) 1495 to a display. Such a display may include, for example, an LCD. SIM interface 1430 may provide access to or from a SIM card or device. SDRAM controller 1440 may provide access to or from memory such as an SDRAM chip or module. Flash controller 1445 may provide access to or from memory such as flash memory or other instances of RAM. SPI master unit 1450 may provide access to or from communications modules, such as a Bluetooth module 1470, high-speed 3G modem 1475, global positioning system module 1480, or wireless module 1485 implementing a communications standard such as 802.11. Instruction set architecture 1400 may further include a power control unit 1455.

FIG. 15 is a more detailed block diagram of an instruction set architecture 1500 of a processor, in accordance with embodiments of the present disclosure. Instruction architecture 1500 may implement one or more aspects of instruction set architecture 1400. Furthermore, instruction set architecture 1500 may illustrate modules and mechanisms for the execution of instructions within a processor.

Instruction architecture 1500 may include a memory system 1540 communicatively coupled to one or more execution entities 1565. Furthermore, instruction architecture 1500 may include a caching and bus interface unit such as unit 1510 communicatively coupled to execution entities 1565 and memory system 1540. In one embodiment, loading of instructions into execution entities 1564 may be performed by one or more stages of execution. Such stages may include, for example, instruction prefetch stage 1530, dual instruction decode stage 1550, register rename stage 155, issue stage 1560, and writeback stage 1570.

In one embodiment, memory system 1540 may include an executed instruction pointer 1580. Executed instruction pointer 1580 may store a value identifying the oldest, undispatched instruction within a batch of instructions. The oldest instruction may correspond to the lowest Program Order (PO) value. A PO may include a unique number of an instruction. Such an instruction may be a single instruction within a thread represented by multiple strands. A PO may be used in ordering instructions to ensure correct execution semantics of code. A PO may be reconstructed by mechanisms such as evaluating increments to PO encoded in the instruction rather than an absolute value. Such a reconstructed PO may be known as an “RPO.” Although a PO may be referenced herein, such a PO may be used interchangeably with an RPO. A strand may include a sequence of instructions that are data dependent upon each other. The strand may be arranged by a binary translator at compilation time. Hardware executing a strand may execute the instructions of a given strand in order according to PO of the various instructions. A thread may include multiple strands such that instructions of different strands may depend upon each other. A PO of a given strand may be the PO of the oldest instruction in the strand which has not yet been dispatched to execution from an issue stage. Accordingly, given a thread of multiple strands, each strand including instructions ordered by PO, executed instruction pointer 1580 may store the oldest—illustrated by the lowest number—PO in the thread.

In another embodiment, memory system 1540 may include a retirement pointer 1582. Retirement pointer 1582 may store a value identifying the PO of the last retired instruction. Retirement pointer 1582 may be set by, for example, retirement unit 454. If no instructions have yet been retired, retirement pointer 1582 may include a null value.

Execution entities 1565 may include any suitable number and kind of mechanisms by which a processor may execute instructions. In the example of FIG. 15, execution entities 1565 may include ALU/multiplication units (MUL) 1566, ALUs 1567, and floating point units (FPU) 1568. In one embodiment, such entities may make use of information contained within a given address 1569. Execution entities 1565 in combination with stages 1530, 1550, 1555, 1560, 1570 may collectively form an execution unit.

Unit 1510 may be implemented in any suitable manner. In one embodiment, unit 1510 may perform cache control. In such an embodiment, unit 1510 may thus include a cache 1525. Cache 1525 may be implemented, in a further embodiment, as an L2 unified cache with any suitable size, such as zero, 128 k, 256 k, 512 k, 1M, or 2M bytes of memory. In another, further embodiment, cache 1525 may be implemented in error-correcting code memory. In another embodiment, unit 1510 may perform bus interfacing to other portions of a processor or electronic device. In such an embodiment, unit 1510 may thus include a bus interface unit 1520 for communicating over an interconnect, intraprocessor bus, interprocessor bus, or other communication bus, port, or line. Bus interface unit 1520 may provide interfacing in order to perform, for example, generation of the memory and input/output addresses for the transfer of data between execution entities 1565 and the portions of a system external to instruction architecture 1500.

To further facilitate its functions, bus interface unit 1510 may include an interrupt control and distribution unit 1511 for generating interrupts and other communications to other portions of a processor or electronic device. In one embodiment, bus interface unit 1510 may include a snoop control unit 1512 that handles cache access and coherency for multiple processing cores. In a further embodiment, to provide such functionality, snoop control unit 1512 may include a cache-to-cache transfer unit 1513 that handles information exchanges between different caches. In another, further embodiment, snoop control unit 1512 may include one or more snoop filters 1514 that monitors the coherency of other caches (not shown) so that a cache controller, such as unit 1510, does not have to perform such monitoring directly. Unit 1510 may include any suitable number of timers 1515 for synchronizing the actions of instruction architecture 1500. Also, unit 1510 may include an AC port 1516.

Memory system 1540 may include any suitable number and kind of mechanisms for storing information for the processing needs of instruction architecture 1500. In one embodiment, memory system 1540 may include a load store unit 1546 for storing information such as buffers written to or read back from memory or registers and a data cache 1542. In another embodiment, memory system 1540 may include a translation lookaside buffer (TLB) 1545 that provides look-up of address values between physical and virtual addresses. In yet another embodiment, bus interface unit 1520 may include a memory management unit (MMU) 1544 for facilitating access to virtual memory. In still yet another embodiment, memory system 1540 may include a prefetcher 1543 for requesting instructions from memory before such instructions are actually needed to be executed, in order to reduce latency.

The operation of instruction architecture 1500 to execute an instruction may be performed through different stages. For example, using unit 1510 instruction prefetch stage 1530 may access an instruction through prefetcher 1543. Instructions retrieved may be stored in instruction cache 1532. Prefetch stage 1530 may enable an option 1531 for fast-loop mode, wherein a series of instructions forming a loop that is small enough to fit within a given cache are executed. In one embodiment, such an execution may be performed without needing to access additional instructions from, for example, instruction cache 1532. Determination of what instructions to prefetch may be made by, for example, branch prediction unit 1535, which may access indications of execution in global history 1536, indications of target addresses 1537, or contents of a return stack 1538 to determine which of branches 1557 of code will be executed next. Such branches may be possibly prefetched as a result. Branches 1557 may be produced through other stages of operation as described below. Instruction prefetch stage 1530 may provide instructions as well as any predictions about future instructions to dual instruction decode stage.

Dual instruction decode stage 1550 may translate a received instruction into microcode-based instructions that may be executed. Dual instruction decode stage 1550 may simultaneously decode two instructions per clock cycle. Furthermore, dual instruction decode stage 1550 may pass its results to register rename stage 1555. In addition, dual instruction decode stage 1550 may determine any resulting branches from its decoding and eventual execution of the microcode. Such results may be input into branches 1557.

Register rename stage 1555 may translate references to virtual registers or other resources into references to physical registers or resources. Register rename stage 1555 may include indications of such mapping in a register pool 1556. Register rename stage 1555 may alter the instructions as received and send the result to issue stage 1560.

Issue stage 1560 may issue or dispatch commands to execution entities 1565. Such issuance may be performed in an out-of-order fashion. In one embodiment, multiple instructions may be held at issue stage 1560 before being executed. Issue stage 1560 may include an instruction queue 1561 for holding such multiple commands. Instructions may be issued by issue stage 1560 to a particular processing entity 1565 based upon any acceptable criteria, such as availability or suitability of resources for execution of a given instruction. In one embodiment, issue stage 1560 may reorder the instructions within instruction queue 1561 such that the first instructions received might not be the first instructions executed. Based upon the ordering of instruction queue 1561, additional branching information may be provided to branches 1557. Issue stage 1560 may pass instructions to executing entities 1565 for execution.

Upon execution, writeback stage 1570 may write data into registers, queues, or other structures of instruction set architecture 1500 to communicate the completion of a given command. Depending upon the order of instructions arranged in issue stage 1560, the operation of writeback stage 1570 may enable additional instructions to be executed. Performance of instruction set architecture 1500 may be monitored or debugged by trace unit 1575.

FIG. 16 is a block diagram of an execution pipeline 1600 for an instruction set architecture of a processor, in accordance with embodiments of the present disclosure. Execution pipeline 1600 may illustrate operation of, for example, instruction architecture 1500 of FIG. 15.

Execution pipeline 1600 may include any suitable combination of steps or operations. In 1605, predictions of the branch that is to be executed next may be made. In one embodiment, such predictions may be based upon previous executions of instructions and the results thereof. In 1610, instructions corresponding to the predicted branch of execution may be loaded into an instruction cache. In 1615, one or more such instructions in the instruction cache may be fetched for execution. In 1620, the instructions that have been fetched may be decoded into microcode or more specific machine language. In one embodiment, multiple instructions may be simultaneously decoded. In 1625, references to registers or other resources within the decoded instructions may be reassigned. For example, references to virtual registers may be replaced with references to corresponding physical registers. In 1630, the instructions may be dispatched to queues for execution. In 1640, the instructions may be executed. Such execution may be performed in any suitable manner. In 1650, the instructions may be issued to a suitable execution entity. The manner in which the instruction is executed may depend upon the specific entity executing the instruction. For example, at 1655, an ALU may perform arithmetic functions. The ALU may utilize a single clock cycle for its operation, as well as two shifters. In one embodiment, two ALUs may be employed, and thus two instructions may be executed at 1655. At 1660, a determination of a resulting branch may be made. A program counter may be used to designate the destination to which the branch will be made. 1660 may be executed within a single clock cycle. At 1665, floating point arithmetic may be performed by one or more FPUs. The floating point operation may require multiple clock cycles to execute, such as two to ten cycles. At 1670, multiplication and division operations may be performed. Such operations may be performed in four clock cycles. At 1675, loading and storing operations to registers or other portions of pipeline 1600 may be performed. The operations may include loading and storing addresses. Such operations may be performed in four clock cycles. At 1680, write-back operations may be performed as required by the resulting operations of 1655-1675.

FIG. 17 is a block diagram of an electronic device 1700 for utilizing a processor 1710, in accordance with embodiments of the present disclosure. Electronic device 1700 may include, for example, a notebook, an ultrabook, a computer, a tower server, a rack server, a blade server, a laptop, a desktop, a tablet, a mobile device, a phone, an embedded computer, or any other suitable electronic device.

Electronic device 1700 may include processor 1710 communicatively coupled to any suitable number or kind of components, peripherals, modules, or devices. Such coupling may be accomplished by any suitable kind of bus or interface, such as I²C bus, system management bus (SMBus), low pin count (LPC) bus, SPI, high definition audio (HDA) bus, Serial Advance Technology Attachment (SATA) bus, USB bus (versions 1, 2, 3), or Universal Asynchronous Receiver/Transmitter (UART) bus.

Such components may include, for example, a display 1724, a touch screen 1725, a touch pad 1730, a near field communications (NFC) unit 1745, a sensor hub 1740, a thermal sensor 1746, an express chipset (EC) 1735, a trusted platform module (TPM) 1738, BIOS/firmware/flash memory 1722, a digital signal processor 1760, a drive 1720 such as a solid state disk (SSD) or a hard disk drive (HDD), a wireless local area network (WLAN) unit 1750, a Bluetooth unit 1752, a wireless wide area network (WWAN) unit 1756, a global positioning system (GPS) 1755, a camera 1754 such as a USB 3.0 camera, or a low power double data rate (LPDDR) memory unit 1715 implemented in, for example, the LPDDR3 standard. These components may each be implemented in any suitable manner.

Furthermore, in various embodiments other components may be communicatively coupled to processor 1710 through the components discussed above. For example, an accelerometer 1741, ambient light sensor (ALS) 1742, compass 1743, and gyroscope 1744 may be communicatively coupled to sensor hub 1740. A thermal sensor 1739, fan 1737, keyboard 1746, and touch pad 1730 may be communicatively coupled to EC 1735. Speaker 1763, headphones 1764, and a microphone 1765 may be communicatively coupled to an audio unit 1764, which may in turn be communicatively coupled to DSP 1760. Audio unit 1764 may include, for example, an audio codec and a class D amplifier. A SIM card 1757 may be communicatively coupled to WWAN unit 1756. Components such as WLAN unit 1750 and Bluetooth unit 1752, as well as WWAN unit 1756 may be implemented in a next generation form factor (NGFF).

Embodiments of the present disclosure involve an instruction and processing logic for detecting numeric accumulation error associated with floating point numbers. FIG. 18 is an illustration of an example embodiment of a system 1800 having an instruction and logic for detecting numeric accumulation error, in accordance with embodiments of the present disclosure. System 1800 may include any suitable number and kind of elements to perform the operations described herein, including a processor, SoC, integrated circuit, or other mechanism. Furthermore, although specific elements of system 1800 may be described herein as performing a specific function, any suitable portion of 1800 may perform the functionality described herein. For example, system 1800 may include processor 1802. Although processor 1802 is shown and described as an example in FIG. 18, any suitable mechanism may be used. Processor 1802 may include any suitable mechanism for detecting numeric accumulation error. In one embodiment, such mechanisms may be implemented in hardware. Processor 1802 may be implemented fully or in part by the elements described in FIGS. 1-17.

In one embodiment, system 1800 may include a numeric accumulation error detection unit (NAEDU) 1826 for floating point arithmetic. System 1800 may include numeric accumulation error detection unit 1826 in any suitable portion of system 1800. In one embodiment, numeric accumulation error detection unit 1826 may be implemented as an execution unit 1822 within an in-order or out-of-order execution pipeline 1816. In another embodiment, numeric accumulation error detection unit 1826 may be implemented within intellectual property (IP) core(s) 1828 separate from main core(s) 1814 of processor 1802. Numeric accumulation error detection unit 1826 may be implemented by any suitable combination of circuitry or hardware computational logic of a processor.

Floating point units may be used in deep-learning, convolutional neural networks (CNN), and/or other applications, including mobile and desktop computing, to represent numbers in scientific notation. This representation may include a sign designator, an exponent, and a mantissa. The mantissa may represent a fraction and an implicit or explicit leading whole number, in which the fraction and whole number are separated by a radix point, such as a decimal point or binary point. As the exponent increases, the scale of the floating point number may also increase, which may result in reduced precision. Floating point applications may perform many iterations of a floating point operation, such as an addition, subtraction, and/or multiplication. When the application begins execution, the exponent may be relatively small, such as near zero or even negative, which may result in increased precision.

For example, a binary floating-point number with an exponent of −5 and a mantissa of 1.1101 may be equal to 0.000011101 with a floating point precision of 2⁻⁹. As the application executes, the exponent may increase, which may result in reduced precision. For example, the binary floating-point number with the mantissa of 1.1101 may eventually have an exponent of 1, or be equal to 11.101 with a floating point precision of 2⁻³. If the operand 1.1101×2⁻⁵ were added to the accumulated value 1.1101×2¹, the new accumulated value may be 1.1101011101×2¹. However, if the new accumulated value were stored with a floating point representation allocating four bits for the mantissa with an implicit leading bit, the four most significant bits (“1101”) of the mantissa in the new accumulated value may be maintained in a floating point result, while the remaining bits (“011101”) of the mantissa in the new accumulated value may be discarded or lost in the floating point result. Thus, the floating point result may be 1.1101×2¹, which may be the same value as the original accumulated value without the addition of the operand. As illustrated by this example, the floating point precision may not be capable of properly representing some values that require additional floating point precision, which may produce an inaccurate result.

Although a floating point application may increase floating point accuracy by increasing the number of bits available to represent a floating point value, such increases may reduce performance and/or require additional power, hardware circuitry, and/or silicon area. Thus, it may be desirable to begin execution of a floating point application with a minimal number of bits in a floating point value, and then increase the number of bits in the floating point value at a later point in time to increase the floating point accuracy if needed. Such an approach with variable floating point accuracy during the execution of a floating point application may reduce power, hardware circuitry, and silicon area, while increasing performance. To facilitate such an approach, processor 1802 may implement a numeric accumulation error detection unit 1826 to inform or notify a floating point application of an inaccurate result. Although a floating point application may determine an inexact result by checking for an inexact exception, such a notification may not provide the application with the flexibility to tune the accuracy of the result to the needs of the application. For example, an application may not be sensitive to results that are inaccurate due to the loss of several bits of data in the mantissa of a floating point result. Such an application may benefit from being able to receive notifications when the inaccuracy exceeds a threshold, rather than to receive notifications when there is any inaccuracy, including an inaccuracy of one bit.

Numeric accumulation error detection unit 1826 may include circuitry to provide the ability to detect, flag, and/or signal a numeric accumulation error caused by a floating point operation. Although the term accumulation is used, numeric accumulation error detection unit 1826 may include circuitry to support the detection of numeric accumulation errors for addition, subtraction, and/or multiplication operations involving floating point numbers. Floating point addition, for example, may involve four steps, including aligning the exponents between the operands, adding the mantissas of the operands, normalizing the result, and rounding of the result. Numeric accumulation error may occur when the result of a floating point operation represents a loss in accuracy of the actual mathematical operation. A loss in accuracy may occur, for instance, when aggregating small values into an increasingly larger sum, in which small values added later in the aggregation may not contribute to the sum. Such a lack of contribution may occur based on the standard scale of the sum, which is represented as a floating point number, and the rounding scheme for floating point operations. As described above, the scale of a floating point number is variable based on the exponent and the size of the mantissa. System 1800 may support any suitable type of floating point rounding scheme including, but not limited to, truncation, rounding up, rounding down, rounding to the nearest even value, rounding away from zero, and rounding toward zero. Numeric accumulation error detection unit 1826 may compare the rounded result to the actual result to determine the number of bits lost. The rounded result may be referred to as a floating point result or rounded floating point result, and the actual result may be referred to as a floating point sum, floating point difference, floating point product, actual floating point result, or raw floating point result.

To facilitate such a notification, numeric accumulation error detection unit 1826 may be tuned to detect errors and provide a notification according to the needs of the application. Numeric accumulation error detection unit 1826 may have a threshold associated with the amount of inaccuracy accepted or required before a numeric accumulation error notification is provided. In one embodiment, the threshold may provide the ability to enable or disable numeric accumulation error detection. In another embodiment, accumulation error detection unit 1826 may have a numeric accumulation error detection flag associated with whether numeric accumulation error detection is enabled. If the flag is set, then numeric accumulation error detection may be enabled, and if the flag is not set, then numeric accumulation error detection may not be enabled. In the alternative, if the flag is set, numeric accumulation error detection may not be enabled, and if the flag is not set, numeric accumulation error detection may be enabled.

The threshold may be defined in any manner suitable to tune the detection and notification of numeric accumulation errors. In one embodiment, the threshold may be a number. If the number of bits of inaccuracy in the mantissa of the floating point result is greater than or equal to the threshold, a numeric accumulation error notification may be provided. The threshold may span a range representing a loss in accuracy of more than one bit. The minimum of the range may be two bits. For example, if one bit in the mantissa of the floating point result is inaccurate, notification of a numeric accumulation error may not be provided. However, if two bits in the mantissa of the floating point result are inaccurate, notification of a numeric accumulation error may be provided. The maximum of the range may be based on the number of bits in the floating point representation of the operands, including the number of bits for the exponent and/or the number of bits for the mantissa, and/or the type of floating point operation. For floating point operations involving multiplication, the floating point product may have a maximum number of bits in the mantissa equivalent to twice as many mantissa bits as the operands. For example, multiplying two floating point values with 10-bit mantissae may result in a floating point product with a 20-bit mantissa. If that floating point result is then represented with a 10-bit mantissa, 10 bits of the 20-bit mantissa from the floating point product may be discarded or lost. For floating point operations involving addition or subtraction, the floating point sum or floating point difference may have a maximum number of bits in the mantissa equivalent to 2^(n), in which n is the number of bits representing the exponent. For example, a floating point difference with an exponent of 8 bits may have a maximum of 2⁸ or 256 bits in the mantissa. If that floating point result is then represented with a 10-bit mantissa, 246 bits of the 256-bit mantissa from the floating point difference may be discarded or lost. In some embodiments, this maximum may be reduced to reserve one or more exponent representations for one or more special values, such as zero, negative zero, infinity, negative infinity, and not a number (NaN). For example, if an exponent of all zeros is reserved for the floating-point representation of the value 0, the maximum number of bits in the mantissa would be one less, or 255 bits. Although mantissae with specific numbers of bits are described, the mantissa may be of any suitable length for floating point representation. Moreover, the span of the range may be further narrowed to reduce the complexity of numeric accumulation error detection unit 1826. For example, the minimum of the range may be more than 2 bits and the maximum of the range may be less than 255 bits. Further, if a numeric accumulation error notification is provided when the number of bits of inaccuracy in the mantissa of the floating point result is greater than the threshold, the range may be adjusted downward by one bit.

In another embodiment, the threshold may be defined as a number corresponding to the percentage of the mantissa that may be inaccurate before a numeric accumulation error notification is provided. For example, the threshold may be a 4-bit value. If the threshold is set to “0000,” numeric accumulation error detection may be disabled. If the threshold is set to “0001,” 10% of the mantissa may be inaccurate before a numeric accumulation error notification is provided. If the threshold is set to “1010,” 100% of the mantissa may be inaccurate before a numeric accumulation error notification is provided. The percentage may correspond to the mantissa of the rounded floating point result or the actual floating point result. The rounded floating point result may have a defined number of bits in its mantissa, while the actual floating point result may have a variable number of bits in its mantissa based on the number of bits in the floating point representation of the operands, including the number of bits for the exponent and/or the number of bits for the mantissa, and/or the type of floating point operation. Accordingly, a threshold set to 100% of the mantissa, for example, may correspond to 100% of the bits in the rounded floating point result's mantissa, or 100% of the actual floating point result's mantissa.

During execution of a floating point application, or any other application, instructions may be received from instruction stream 1804, which may reside within a memory subsystem of system 1800. Instruction stream 1804 may be included in any suitable portion of processor 1802 or system 1800. In one embodiment, instruction stream 1804A may be included in an SoC, system, or other mechanism. In another embodiment, instruction stream 1804B may be included in a processor, integrated circuit, or other mechanism. Processor 1802 may include a front end 1806 to receive or retrieve instructions from any suitable location, including a cache or memory. Instructions may include instruction stream 1804. Front end 1806 may include a fetcher 1808 to fill the pipeline efficiently with possible instructions to execute. Front end 1806 may include an instruction decoder 1810 to decode an instruction into opcodes for execution, which may determine the meaning, side effects, data required, data consumed, and data to be produced for the instruction. A binary translator 1812 may be used to optimize or improve the efficiency of code.

The decoded instructions may be passed to an out-of-order or in-order execution unit in an execution pipeline 1816. Execution pipeline 1816 may include a rename and allocate unit 1818 for renaming instructions for out-of-order execution, and a reorder buffer (ROB) coextensive with a retirement unit 1824 so that instructions may appear to be retired in the order that they were received. Rename and allocate unit 1818 may further rename or allocate resources for execution of multiple instructions in parallel. Scheduler 1820 may schedule or allocate instructions to execute on execution units 1822 when inputs are available. Outputs of execution units 1822 may queue in the ROB 1824. Front end 1806 may attempt to anticipate any behaviors that will prevent instructions from executing in a sequential stream and may fetch streams of instructions that might execute. When there is, for example, a misprediction of a branch, the ROB 1824 may inform the front-end 1806 and a different set of instructions might be executed instead. Front end 1806 may store data such as metadata for branch prediction. The instructions may be retired as if they were executed in program order. Various portions of such execution pipelining may be performed by one or more cores 1814. Each core 1814 may include one or more threads or logical cores for execution.

The execution units 1822, which may include a floating point unit, may communicate with a numeric accumulation error detection unit 1826. Although numeric accumulation error detection unit 1826 is described as a portion of a core, the circuitry may reside in any suitable portion of processor 1802, including but not limited to IP Core(s) 1828. processor 1802 may recognize, either implicitly or through decoding and execution of specific instructions, that a floating point computation needs to be checked for numeric accumulation error. In such cases, the check may be offloaded to numeric accumulation error detection unit 1826. In one embodiment, numeric accumulation error detection unit 1826 may be targeted by specific instructions to be executed in instruction stream 1804. Such specific instructions may be generated by, for example, a compiler, or may be designed by a drafter of code resulting in instruction stream 1804. The instruction may be included in a library defined for execution by processor 1802 or numeric accumulation error detection unit 1826. In another embodiment, numeric accumulation error detection unit 1826 may be targeted by portions of processor 1802. For example, when processor 1802 recognizes an attempt in instruction stream 1804 to execute a floating-point instruction with a desired precision or threshold for detecting numeric accumulation error, processor 1802 may direct the floating-point instruction to numeric accumulation error detection unit 1826, or may direct execution unit(s) 1822 to interface with numeric accumulation error detection unit 1826.

Instructions 1830 may represent floating point operations that may configure or use numeric accumulation error detection unit 1826. A numeric accumulation error precision (NAEP) control, which may also be referred to as a threshold, may be defined using a separate instruction or by including an extra operand in an instruction calculating a floating-point result. The threshold may indicate the amount of precision to be lost in the mantissa of the floating point result before notification of a numeric accumulation error is provided. The amount of precision to be lost in the mantissa may correspond to a minimum of two bits to be lost before notification of the error is provided. In one embodiment, the threshold may define the number of bits to be lost before a numeric accumulation error notification is provided. For example, a threshold setting of 8 may require a precision loss of 8 bits before a numeric accumulation error is indicated. In another embodiment, the threshold may define the percentage of total bits to be lost before a numeric accumulation error notification is provided. For example, a threshold setting of 20% may require a loss of 20 bits in a 100-bit mantissa before a numeric accumulation error is indicated.

Moreover, a numeric accumulation error for non-zero bits (NAENZ) control, which may be a bit or flag, may be defined using the same instruction used to set NAEP, a separate instruction, or by including an extra operand in an instruction calculating a floating-point result. The NAENZ control may modify detection of the numeric accumulation error. A value of 1 may correspond to modification and a value of 0 may correspond to no modification, or a value of 1 may correspond to no modification and a value of 0 may correspond to modification. In one embodiment, the NAENZ control may modify the detection of a numeric accumulation error by not counting trailing bits with the value of zero when determining whether a numeric accumulation error occurred. In another embodiment, the NAENZ control may modify the detection of a numeric accumulation error by not counting any bits with the value of zero that reside in the bits that are lost when the actual floating point result becomes the rounded floating point result.

In one embodiment, a SETCONTROLFPQQ instruction with NAEP and/or NAENZ control parameters may define the appropriate field or fields in a control register associated with numeric accumulation error control or with floating point unit control. In another embodiment, an instruction with a floating-point result may include NAEP and/or NAENZ control parameters. For example, basic floating-point instructions, such as FADD, FADDP, FIADD, FSUB, FSUBP, FISUB, FMUL, FMULP, and FIMUL, may include NAEP and/or NAENZ control parameters in addition to the typical operands, which may include two source floating-point registers and a destination floating-point register. Similarly, the ADD, SUB, and MUL instructions, or the vector forms of these instructions, VADD, VSUB, and VMUL, can include NAEP and/or NAENZ control parameters. These parameters may be included regardless of the data type of the operation, including scalar single-precision (SS), scalar double-precision (SD), packed single-precision (PS), and packed double-precision (PD). Likewise, complex arithmetic instructions, such as ADDSUBPD and ADDSUBPS, may include NAEP and/or NAENZ parameters. Finally, fused multiply-add (FMA) instructions, such as VFMADD, VFNMADD, VFMSUB, VFNMSUB, VFMADDSUB, and VFMSUBADD, may include NAEP and/or NAENZ control parameters to configure numeric accumulation error detection, including the threshold for detecting numeric accumulation errors and the non-zero control for modifying the detection of numeric accumulation errors. The FMA instructions may include any suitable data type, including those listed for vector instructions above. The FMA instruction may also include any suitable number of source operands and any suitable order in which to process the source operands, including an FMA instruction that may compute the floating point sum of two source operands and then may compute the floating point product of the floating point sum and a third source operand. These parameters, NAEP and/or NAENZ, along with any other parameters of the instructions defining a floating-point result, may be in any suitable form, including parameter flags for the floating point instruction, explicit parameters, required parameters, optional parameters with an assumed default value, or inherent parameters stored in registers or other known locations that do not require the information to be explicitly passed as a parameter.

Although various operations are described in this disclosure as performed by specific components of processor 1802, the functionality may be performed by any suitable portion of processor 1802.

FIG. 19A illustrates a block diagram with selected elements from a floating point unit for accumulating floating point numbers, in accordance with embodiments of the present disclosure. Although accumulation with addition is shown, numeric accumulation errors may occur with any suitable floating point operation, including addition, subtraction, and/or multiplication. Accumulation of floating point numbers may occur in floating point unit 1900, which may include a floating point addition unit 1918A. Floating point addition unit 1918A may have one floating point output, which may be new accumulated value 1920, and two floating point inputs: operand 1902A and old accumulated value 1912. Although two inputs are shown, floating point addition unit 1918A may support any suitable number of inputs for floating point addition.

Operand 1902A may include an exponent 1904A and a mantissa 1906A. The exponent may be an absolute value, or may represent an offset from an absolute value. The mantissa may include an implicit or explicit leading whole number, such as an integer. In the example shown in FIG. 19A, operand 1902A includes exponent 1904A with a value of 7, and mantissa 1906A with a value of 1.1001010110. Thus, operand 1902A may be represented as 1.1001010110×2⁷, or 11001010.110. Although an exponent of 7 and a particular mantissa is shown, any exponent or mantissa suitable for floating point representation may be used.

Operand 1902A may be added to old accumulated value 1912, which may include exponent 1914 and mantissa 1916. Exponent 1914 may have a value of 15, and mantissa 1916 may have a value of 1.1101111011. Old accumulated value 1912 may be represented as 1.1101111011×2¹⁵, or 111011110110000, which represents the value 30,640 in decimal. Old accumulated value 1912 may have originally been a smaller number that increased in value over time as additional floating point numbers were accumulated together. Although old accumulated value is shown with an exponent of 15 and a specific mantissa, any exponent or mantissa suitable for floating point representation may be used.

As noted above, floating point addition may include four steps. The first step may include aligning the exponents of the source operands. FIG. 19B illustrates a block diagram with selected elements from an execution unit for detecting numeric accumulation error in floating point numbers with aligned exponents, in accordance with embodiments of the present disclosure. For example, accumulation of floating point numbers may occur in an execution unit 1930, such as execution unit(s) 1822, floating point unit, or numeric accumulation error detection unit 1826, which may include a floating point addition unit 1918B that expects floating point source operands with aligned exponents. Although unit 1918B expects aligned exponents, unit 1918B may perform the alignment of the exponents itself.

The alignment of exponents between source floating point operands may require the adjustment of the exponent and mantissa for one or more inputs. In the example shown, inputs with smaller exponents may be aligned with the input having the largest exponent. Although such an alignment to the largest value is shown, it may be possible to align to the lowest input or to an input falling between other inputs in magnitude. Operand 1902B, for instance, is shown with an aligned exponent 1904B and an aligned mantissa 1906B. Aligned exponent 1904B is the same value as the exponent 1914 for the old accumulated value input 1912. After alignment, aligned mantissa 1906B has a leading digit or bit of 0. Mantissa 1906A is shown shifted to the right by the difference between the exponents (i.e., 15−7=8). Accordingly, mantissa 1906B includes eight leading zeros and the original mantissa as 1910.

Operand 1902B may be added to old accumulated value 1912 to produce new accumulated value 1920. New accumulated value 1920 may have an exponent 1922, shown with a value of 15, and a mantissa 1926. Mantissa 1926 may need to be rounded to store the result, such that the new accumulated value has the same size representation as the old accumulated value. The rounding may result in only a portion of the mantissa being stored. For example, the most significant portion 1924 of mantissa 1926 may be retained while the least significant portion 1928 may be lost. After rounding, the new accumulated value 1920 may include exponent 1922 and the most least significant portion of the mantissa 1924, and may exclude the least significant portion of the mantissa 1928. In this case, only three bits (1908) from operand 1902B may affect the new accumulated value 1920. Although rounding is shown as truncation of the mantissa, any suitable form of rounding may be performed, including rounding up, rounding down, rounding to the nearest even value, rounding away from zero, and rounding toward zero.

While an absolute loss in precision may be handled by signaling that the result is inexact, such a signal does not define the significance of the loss, or the number of bits lost. Some floating point applications may be fault tolerant, in which a loss of several bits of precision, such as the eight bits in the least significant portion of the mantissa 1926, is not important. Accordingly, a numeric accumulation error detection unit may include NAEP control and NAENZ control to direct how many bits in the least significant portion of the mantissa of the rounded floating point result can be lost before an error notification is provided. In the example shown, if the NAEP control directs that 8 bits can be lost, the numeric accumulation error detection unit may not indicate an error for new accumulated value 1920. However, if the NAEP control directs that 3 bits can be lost, the numeric accumulation error detection unit may indicate an error for new accumulated value 1920 because more than three bits are lost in the rounded floating point result. Although this illustration shows NAEP control directing that 3 bits and 8 bits can be lost, NAEP control may direct any number of bits equal to or greater than 2 bits can be lost for floating point operations. Moreover, although a fixed number of bits is illustrated, the NAEP control may be defined as a percentage of the mantissa for the rounded floating point result or the actual floating point result.

An application using floating point operations may use lower-precision floating point values until an exception is raised due to the detection of a numeric accumulation error or until the application checks a register with a flag whose value indicates a numeric accumulation error. In one embodiment, the application may respond to the exception by using higher-precision floating point values. In another embodiment, the application may store the result prior to the numeric accumulation error in an intermediate location, and use the stored result in an operation resulting in a higher-precision floating point result.

As noted previously, although a floating point addition operation is shown in FIGS. 19A and 19B, any suitable operation for floating point applications may be used, including addition, subtraction, and/or multiplication. Multiplication, for example, may result in even greater losses in information stored in the mantissae of the source operands. Multiplication may result in a mantissa of the product that is twice the size of the source mantissae (e.g., two floating point numbers with a mantissa of 10-bits would result in a product with a mantissa of 20-bits). To store the product with the same sized floating point representation as the operands, the lower half of the mantissa may be discarded. Before being discarded, the numeric accumulation error detection unit may evaluate the discarded bits of the mantissa to determine whether to provide notification of a numeric accumulation error. In one embodiment, the evaluation may include determining the number of bits discarded from the mantissa. In another embodiment, the evaluation may include determining the number of non-zero bits discarded from the mantissa. In a further embodiment, the evaluation may include determining the number of leading non-zero bits discarded from the mantissa. For example, the evaluation may ignore the trailing non-zero bits discarded from the mantissa and may then determine the number of bits discarded.

FIG. 20 is a block diagram of an example method 2000 for detecting an numeric accumulation error, according to embodiments of the present disclosure. Method 2000 may be implemented by any of the elements shown in FIGS. 1-19. Method 2000 may be initiated by any suitable criteria and may initiate operation at any suitable point. In one embodiment, method 2000 may initiate operation at 2005. Method 2000 may include greater or fewer steps than those illustrated. Moreover, method 2000 may execute its steps in an order different than those illustrated in FIG. 20. Method 2000 may terminate at any suitable step. Furthermore, method 2000 may repeat operation at any suitable step. Method 2000 may perform any of its steps in parallel with other steps of method 2000, or in other methods.

At 2005, in one embodiment at least one instruction, which may compute a floating point result, may be received. The instructions may be received, decoded, and executed. The instructions may specify that numeric accumulation error detection unit 1826 is to determine whether numeric accumulation error occurred during the execution of the instruction. In another embodiment, an explicit instruction may be received to enable detection of numeric accumulation error before an instruction to compute a floating-point result. The explicit instruction may be received, decoded, and executed.

In one embodiment, an instruction may specifically designate handling by a numeric accumulation error detection unit 1826. In another embodiment, it may be determined that an instruction can be handled by a numeric accumulation error detection unit. Inputs relevant to detecting numeric accumulation error may be handed off to a numeric accumulation error detection unit for processing. Method step 2005 may be performed by, for instance, a front end, a core, an execution unit, or other suitable elements of a processor.

At 2010, in one embodiment a numeric accumulation error precision threshold may be determined. The determination may be based on the instruction, a previous instruction, or a floating point control register. A detected numeric accumulation error may need to be equal to or greater than the threshold in order for method 2000 to provide notification that a numeric accumulation error has occurred. Notification may include any suitable mechanism, including signaling an interrupt or writing a value to a flag. In one embodiment, the threshold may be static or fixed by the processor using any suitable mechanism, including circuitry and microcode. If the threshold is static or fixed, method 2000 may not need to determine its value. For example, if the threshold is fixed to the value of 2, method 200 would not need to determine its value. Rather, for a numeric accumulation error precision threshold of 2, method 2000 would be able to provide notification of a numeric accumulation error if the amount of precision lost is equal to or greater than 2 bits. Although 2 bits are described, the threshold may be static or fixed to any suitable value compared to the amount of precision lost in the mantissa of the floating point result, in which the amount of precision lost may correspond to a plurality of bits lost in the mantissa of the floating point result. In another embodiment, the threshold may be determined from a general purpose register. In further embodiment, the threshold may be determined from a field in the floating point control register. In yet another embodiment, the threshold may be determine from an immediate value associated with the at least one instruction. The threshold may represent any suitable type of limit corresponding to an amount of precision lost in the mantissa of the floating point result, including the number of bits lost and the percentage of bits lost.

At 2015, in one embodiment a numeric accumulation error non-zero precision flag may be determined. The determination may be based on the instruction, a previous instruction, or a floating point result. The determination may occur in the numeric accumulation error detection unit 1826 or in any other suitable part of processor 1802, including execution unit(s) 1822. The non-zero precision flag may indicate that all types of data should be monitored or non-zero data should be monitored. A flag set to monitor all types of data may detect numeric accumulation errors for bits that are either zero or one in value. A flag set to monitor non-zero data may detect numeric accumulation errors for bits that are non-zero. The bits with a value of zero may be ignored by any suitable mechanism, including masking of the bits or shifting of the bits. In one embodiment, the non-zero precision flag may be used to control whether to ignore at least one trailing bit, or at least one least significant bit, of the mantissa of the floating point result with a value of zero. In another embodiment, the non-zero precision flag may be used to control whether to ignore bits of the mantissa of the floating point result with a value of zero, whether the bits associated with the least significant bits in the mantissa or the most significant bits in the mantissa.

At 2020, in one embodiment a floating point operation may be performed to determine a floating point result. The floating point operation may be computed by an execution unit, such as a floating point unit, or by logic in the IP cores 1828. Accordingly, the floating point result, including the associated floating point exponent and mantissa, may be a function of the related calculation. The related calculation may include the addition, subtraction, and/or multiplication of source values in which the result may use floating point representation. At 2025, the floating point result may be rounded. Rounding may enable the floating point result to be represented in floating point format with a limited number of bits. For example, the number of bits for the floating point format may be limited to the same number of bits as the operands of the floating point operation. Rounding may include any suitable form of rounding, including truncation, rounding up, rounding down, rounding to the nearest even value, rounding away from zero, and rounding toward zero. At 2030, the rounded floating point result may be stored. Storage may include any suitable location, including a temporary location, a register, a cache, a queue, or in a memory subsystem. Storage may further reduce the number of bits representing the floating point value. For example, a 64-bit floating point result may be reduced to 32-bits for storage.

At 2035, in one embodiment it may be determined whether a non-zero precision flag is set to monitor non-zero data. Method 2000 may proceed to method step 2045 if the flag is set. Otherwise, method 2000 may proceed to method step 2040. At 2040, in one embodiment the amount of precision lost for all types of data in the result of the floating point operation may be computed. The computation may involve rounding the result of the floating point operation before computing the amount of precision lost. The rounding of the result may use the same or a different rounding mode as the one performed on the result before storing the result. In one embodiment, computing the amount of precision lost may include counting the number of bits of precision lost. In another embodiment, computing the amount of precision lost may include computing a percentage of bits of precision lost, which may include counting the number of bits of precision lost and dividing such a count by the total number of bits in the floating point mantissa, or in any other portion of a floating point number. At 2045, in one embodiment the amount of non-zero precision lost in the result of the floating point operation may be computed. In one embodiment, the trailing bits of the result of the floating point operation may be truncated before computing the amount of precision lost in the result of the floating point operation. In another embodiment, computing the amount of precision lost may include counting the number of non-zero bits lost in the result.

At 2050, in one embodiment it may be determined whether the amount of precision lost is greater than the threshold, which may be determined in method step 2010. The threshold may default to zero, which may disable numeric accumulation error detection, or to value corresponding to the amount of precision lost before notification of a numeric accumulation error is provided. Although a comparison of greater than or equal to is described, the comparison may be any type of comparison suitable to determine whether a threshold is met and/or exceeded, including comparisons for values less than, less than or equal to, or greater than or equal to the threshold. The comparison may involve comparing two numbers or two percentages corresponding to an amount of precision lost. Method 2000 may proceed to method step 2070 if the amount of precision lost is not greater than the threshold. Otherwise, a numeric accumulation error has occurred and method 2000 may proceed to method step 2055.

At 2055, in one embodiment a value may be written to a flag, which may be for notification that a numeric accumulation error has occurred. The value may be based on the determination that a numeric accumulation error occurred. The flag may be initialized for all floating point instructions to indicate that no numeric accumulation error occurred and then may be updated after a floating point operation using numeric accumulation error detection unit 1826. The flag may reside within a status register field, which may correspond to the execution of floating point instructions. A programmer may check the status of the flag in the status register field to determine the presence of the numeric accumulation error. In one embodiment, the flag may include a register containing the amount of precision lost, which may represent the number of bits of precision lost or a percentage of precision lost. For example, if three bits of precision are lost, the register may include a value indicating that three bits are lost.

An application or programmer may use the status of the flag, or the register information to continue execution. In one embodiment, the application or programmer may respond to a numeric accumulation error by switching execution to floating point operations with a higher precision. For instance, if a numeric accumulation error occurs as a result of a 64-bit floating point operation, the application or programmer may switch to computing 128-bit floating point results. In another embodiment, the application or programmer may respond to a numeric accumulation error by storing the previous or old accumulation value in an intermediate location, such as a register, cache, or memory, and may continue performing floating point operations with the same precision. For example, if a numeric accumulation error occurs as a result of a 64-bit floating point operation, the application or programmer may store the previous result, before the operation that caused the numeric accumulation error, in an intermediate location, and may begin performing 64-bit floating point operations with an initialized value. If the floating point operation is floating point addition, for instance, the initialized value may be zero. The application or programmer may then perform a 128-bit floating point operation including the intermediate value and the floating point result corresponding to the initialized value.

At 2060, in one embodiment, it may be determined whether a mask bit is set to control whether to signal a numeric accumulation error exception. The mask bit may be set by the complier of the code or the drafter of the code using any suitable mechanism including parameter flags for the floating point instruction, explicit parameters, required parameters, optional parameters with an assumed default value, or inherent parameters stored in registers or other known locations that do not require the information to be explicitly passed as a parameter. The mask bit may reside in a control field, such as in the MXCSR control field, corresponding to the execution of floating point instructions.

At 2065, in one embodiment a numeric accumulation error may be signaled by reporting an exception based on the determination that the mask bit is not set. If the mask bit is set, however, the numeric accumulation error may not be reported. In one embodiment, the value written in method step 2055 may be controlled by a separate mechanism, such as the numeric accumulation error precision threshold, than the signaling of an exception in method step 2065. In another embodiment, the mask bit may control both the value written in method step 2055 and the signaling of an exception in method step 2065.

At 2070, the instruction may be retired by, for example, a retirement unit. Method 2000 may optionally repeat or terminate.

Embodiments of the mechanisms disclosed herein may be implemented in hardware, software, firmware, or a combination of such implementation approaches. Embodiments of the disclosure may be implemented as computer programs or program code executing on programmable systems comprising at least one processor, a storage system (including volatile and non-volatile memory and/or storage elements), at least one input device, and at least one output device.

Program code may be applied to input instructions to perform the functions described herein and generate output information. The output information may be applied to one or more output devices, in known fashion. For purposes of this application, a processing system may include any system that has a processor, such as, for example; a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), or a microprocessor.

The program code may be implemented in a high level procedural or object oriented programming language to communicate with a processing system. The program code may also be implemented in assembly or machine language, if desired. In fact, the mechanisms described herein are not limited in scope to any particular programming language. In any case, the language may be a compiled or interpreted language.

One or more aspects of at least one embodiment may be implemented by representative instructions stored on a machine-readable medium which represents various logic within the processor, which when read by a machine causes the machine to fabricate logic to perform the techniques described herein. Such representations, known as “IP cores” may be stored on a tangible, machine-readable medium and supplied to various customers or manufacturing facilities to load into the fabrication machines that actually make the logic or processor.

Such machine-readable storage media may include, without limitation, non-transitory, tangible arrangements of articles manufactured or formed by a machine or device, including storage media such as hard disks, any other type of disk including floppy disks, optical disks, compact disk read-only memories (CD-ROMs), compact disk rewritables (CD-RWs), and magneto-optical disks, semiconductor devices such as read-only memories (ROMs), random access memories (RAMs) such as dynamic random access memories (DRAMs), static random access memories (SRAMs), erasable programmable read-only memories (EPROMs), flash memories, electrically erasable programmable read-only memories (EEPROMs), magnetic or optical cards, or any other type of media suitable for storing electronic instructions.

Accordingly, embodiments of the disclosure may also include non-transitory, tangible machine-readable media containing instructions or containing design data, such as Hardware Description Language (HDL), which defines structures, circuits, apparatuses, processors and/or system features described herein. Such embodiments may also be referred to as program products.

In some cases, an instruction converter may be used to convert an instruction from a source instruction set to a target instruction set. For example, the instruction converter may translate (e.g., using static binary translation, dynamic binary translation including dynamic compilation), morph, emulate, or otherwise convert an instruction to one or more other instructions to be processed by the core. The instruction converter may be implemented in software, hardware, firmware, or a combination thereof. The instruction converter may be on processor, off processor, or part-on and part-off processor.

Thus, techniques for performing one or more instructions according to at least one embodiment are disclosed. While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on other embodiments, and that such embodiments not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art upon studying this disclosure. In an area of technology such as this, where growth is fast and further advancements are not easily foreseen, the disclosed embodiments may be readily modifiable in arrangement and detail as facilitated by enabling technological advancements without departing from the principles of the present disclosure or the scope of the accompanying claims.

In some embodiments of the present disclosure, a processor may include circuitry to decode at least one instruction and an execution unit. The instruction may be to compute a floating point result. The execution unit may include circuitry to execute the instruction to determine the floating point result, compute an amount of precision lost in a mantissa of the floating point result, compare the amount of precision lost to a numeric accumulation error precision threshold, determine whether the numeric accumulation error occurred, and write a value to a flag based on the determination that the numeric accumulation error occurred. The amount of precision lost may correspond to a plurality of bits lost in a mantissa of the floating point result. The determination whether the numeric accumulation error occurred may be based on the comparison between the amount of precision lost in the mantissa of the floating point result and the numeric accumulation error precision threshold. The flag may be for notification that the numeric accumulation error occurred.

In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine the numeric accumulation error precision threshold based on the instruction, a previous instruction, or a floating point control register. The comparison between the amount of precision lost and the numeric accumulation error precision threshold may be based on the numeric accumulation error precision threshold that is determined. In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine whether a mask bit is set to prevent signaling of the numeric accumulation error and signal an exception based on the determination that the mask bit is not set and based on the determination that the numeric accumulation error occurred. In combination with any of the above embodiments, in an embodiment the execution unit includes circuitry to round the floating point result and store the rounded floating point result. The amount of precision lost in the mantissa of the floating point result may represent a percentage of bits in the mantissa of the floating point result that may be lost. The percentage of bits that may be lost may include a percentage of bits that may be lost when the floating point result is rounded and/or a percentage of bits that may be lost when the rounded floating point result is stored. In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine a numeric accumulation error non-zero precision flag and to control whether to ignore at least one trailing bit of the mantissa of the floating point result with a value of zero. The numeric accumulation error non-zero precision flag may be based on the instruction, a previous instruction, or a floating point control register. The circuitry to control may use the numeric accumulation error non-zero precision flag. The computation of the amount of precision lost in the mantissa of the floating point result may be based on the numeric accumulation error non-zero precision flag. In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine a numeric accumulation error non-zero precision flag and to control whether to ignore bits of the mantissa of the floating point result with a value of zero. The numeric accumulation error non-zero precision flag may be based on the instruction, a previous instruction, or a floating point control register. The circuitry to control may use the numeric accumulation error non-zero precision flag. The computation of the amount of precision lost in the mantissa of the floating point result may be based on the numeric accumulation error non-zero precision flag. In combination with any of the above embodiments, in an embodiment the floating point result may be computed from source values and the instruction may be a fused multiply-add instruction. The circuitry to execute the instruction may include circuitry to compute a sum based on the source values and compute the floating point result based on the sum and at least one of the source values.

In some of the present embodiments, a method may include decoding at least one instruction, the instruction for computing a floating point result, executing the instruction to determine the floating point result, computing the amount of precision lost in a mantissa of the floating point result, comparing the amount of precision lost in the mantissa of the floating point result to a numeric accumulation error precision threshold, determining whether the numeric accumulation error occurred, and writing a value to a flag. The amount of precision lost may correspond to a plurality of bits lost in the mantissa of the floating point result. Determining whether the numeric accumulation error occurred may be based on the comparison between the amount of precision lost and the numeric accumulation error precision threshold. The value to be written to the flag may be based on the determination the numeric accumulation error occurred. The flag may be for notification that the numeric accumulation error occurred.

In combination with any of the above embodiments, the method may include determining the numeric accumulation error precision threshold based on the instruction, a previous instruction, or a floating point control register. The comparison between the amount of precision lost and the numeric accumulation error precision threshold may use the numeric accumulation error precision threshold that is determined. In combination with any of the above embodiments, in an embodiment the method may include determining whether a mask bit is set to prevent signaling of the numeric accumulation error and signaling an exception based on the determination that the mask bit is not set and based on the determination that the numeric accumulation error occurred. In combination with any of the above embodiments, in an embodiment the method may include rounding the floating point result and storing the rounded floating point result. The amount of precision lost in the mantissa of the floating point result may represent a percentage of bits in the mantissa of the floating point result that may be lost. The percentage of bits that may be lost may include a percentage of bits that may be lost when rounding the floating point result or a percentage of bits that may be lost when storing the rounded floating point result. In combination with any of the above embodiments, in an embodiment the method may include determining a numeric accumulation error non-zero precision flag and controlling whether to ignore at least one trailing bit of the mantissa with a value of zero. Determining the numeric accumulation error non-zero precision flag may be based on the instruction, a previous instruction, or a floating point control register. Controlling whether to ignore at least one trailing bit of the mantissa may use the numeric accumulation error non-zero precision flag. Computing the amount of precision lost in the mantissa of the floating point result may be based on the numeric accumulation error non-zero precision flag. In combination with any of the above embodiments, in an embodiment the method may include determining a numeric accumulation error non-zero precision flag and controlling whether to ignore bits of the mantissa of the floating point result with a value of zero. Determining the numeric accumulation error non-zero precision flag may be based on the instruction, a previous instruction, or a floating point control register. Controlling whether to ignore at least one trailing bit of the mantissa may use the numeric accumulation error non-zero precision flag. Computing the amount of precision lost in the mantissa of the floating point result may be based on the numeric accumulation error non-zero precision flag. In combination with any of the above embodiments, in an embodiment the floating point result may be computed from source values and the instruction may be a fused multiply-add instruction. Executing the instruction may include computing a sum based on the source values and computing the floating point result based on the sum and at least one of the source values.

In some embodiments of the present disclosure, a system may include circuitry to decode at least one instruction and an execution unit. The instruction may be to compute a floating point result. The execution unit may include circuitry to execute the instruction to determine the floating point result, compute an amount of precision lost in a mantissa of the floating point result, compare the amount of precision lost to a numeric accumulation error precision threshold, determine whether the numeric accumulation error occurred, and write a value to a flag based on the determination that the numeric accumulation error occurred. The amount of precision lost may correspond to a plurality of bits lost in a mantissa of the floating point result. The determination whether the numeric accumulation error occurred may be based on the comparison between the amount of precision lost in the mantissa of the floating point result and the numeric accumulation error precision threshold. The flag may be for notification that the numeric accumulation error occurred.

In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine the numeric accumulation error precision threshold based on the instruction, a previous instruction, or a floating point control register. The comparison between the amount of precision lost and the numeric accumulation error precision threshold may be based on the numeric accumulation error precision threshold that is determined. In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine whether a mask bit is set to prevent signaling of the numeric accumulation error and signal an exception based on the determination that the mask bit is not set and based on the determination that the numeric accumulation error occurred. In combination with any of the above embodiments, in an embodiment the execution unit includes circuitry to round the floating point result and store the rounded floating point result. The amount of precision lost in the mantissa of the floating point result may represent a percentage of bits in the mantissa of the floating point result that may be lost. The percentage of bits that may be lost may include a percentage of bits that may be lost when the floating point result is rounded and/or a percentage of bits that may be lost when the rounded floating point result is stored. In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine a numeric accumulation error non-zero precision flag and to control whether to ignore at least one trailing bit of the mantissa of the floating point result with a value of zero. The numeric accumulation error non-zero precision flag may be based on the instruction, a previous instruction, or a floating point control register. The circuitry to control may use the numeric accumulation error non-zero precision flag. The computation of the amount of precision lost in the mantissa of the floating point result may be based on the numeric accumulation error non-zero precision flag. In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine a numeric accumulation error non-zero precision flag and to control whether to ignore bits of the mantissa of the floating point result with a value of zero. The numeric accumulation error non-zero precision flag may be based on the instruction, a previous instruction, or a floating point control register. The circuitry to control may use the numeric accumulation error non-zero precision flag. The computation of the amount of precision lost in the mantissa of the floating point result may be based on the numeric accumulation error non-zero precision flag. In combination with any of the above embodiments, in an embodiment the floating point result may be computed from source values and the instruction may be a fused multiply-add instruction. The circuitry to execute the instruction may include circuitry to compute a sum based on the source values and compute the floating point result based on the sum and at least one of the source values.

In some embodiments of the present disclosure, an execution unit may include circuitry to execute at least one instruction to determine the floating point result, compute an amount of precision lost in a mantissa of the floating point result, compare the amount of precision lost to a numeric accumulation error precision threshold, determine whether the numeric accumulation error occurred, and write a value to a flag based on the determination that the numeric accumulation error occurred. The amount of precision lost may correspond to a plurality of bits lost in a mantissa of the floating point result. The determination whether the numeric accumulation error occurred may be based on the comparison between the amount of precision lost in the mantissa of the floating point result and the numeric accumulation error precision threshold. The flag may be for notification that the numeric accumulation error occurred.

In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine the numeric accumulation error precision threshold based on the instruction, a previous instruction, or a floating point control register. The comparison between the amount of precision lost and the numeric accumulation error precision threshold may be based on the numeric accumulation error precision threshold that is determined. In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine whether a mask bit is set to prevent signaling of the numeric accumulation error and signal an exception based on the determination that the mask bit is not set and based on the determination that the numeric accumulation error occurred. In combination with any of the above embodiments, in an embodiment the execution unit includes circuitry to round the floating point result and store the rounded floating point result. The amount of precision lost in the mantissa of the floating point result may represent a percentage of bits in the mantissa of the floating point result that may be lost. The percentage of bits that may be lost may include a percentage of bits that may be lost when the floating point result is rounded and/or a percentage of bits that may be lost when the rounded floating point result is stored. In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine a numeric accumulation error non-zero precision flag and to control whether to ignore at least one trailing bit of the mantissa of the floating point result with a value of zero. The numeric accumulation error non-zero precision flag may be based on the instruction, a previous instruction, or a floating point control register. The circuitry to control may use the numeric accumulation error non-zero precision flag. The computation of the amount of precision lost in the mantissa of the floating point result may be based on the numeric accumulation error non-zero precision flag. In combination with any of the above embodiments, in an embodiment the execution unit may include circuitry to determine a numeric accumulation error non-zero precision flag and to control whether to ignore bits of the mantissa of the floating point result with a value of zero. The numeric accumulation error non-zero precision flag may be based on the instruction, a previous instruction, or a floating point control register. The circuitry to control may use the numeric accumulation error non-zero precision flag. The computation of the amount of precision lost in the mantissa of the floating point result may be based on the numeric accumulation error non-zero precision flag. In combination with any of the above embodiments, in an embodiment the floating point result may be computed from source values and the instruction may be a fused multiply-add instruction. The circuitry to execute the instruction may include circuitry to compute a sum based on the source values and compute the floating point result based on the sum and at least one of the source values.

In some of the present embodiments, an apparatus may include a means for decoding at least one instruction, the instruction a means for computing a floating point result, a means for executing the instruction to determine the floating point result, a means for computing the amount of precision lost in a mantissa of the floating point result, a means for comparing the amount of precision lost in the mantissa of the floating point result to a numeric accumulation error precision threshold, a means for determining whether the numeric accumulation error occurred, and a means for writing a value to a flag. The amount of precision lost may correspond to a plurality of bits lost in the mantissa of the floating point result. The means for determining whether the numeric accumulation error occurred may be based on the means for comparing the amount of precision lost to the numeric accumulation error precision threshold. The value to be written to the flag may be based on the determination the numeric accumulation error occurred. The flag may be a means for notification that the numeric accumulation error occurred.

In combination with any of the above embodiments, the apparatus may include a means for determining the numeric accumulation error precision threshold based on the instruction, a previous instruction, or a floating point control register. The means for comparing the amount of precision lost to the numeric accumulation error precision threshold may use the numeric accumulation error precision threshold that is determined. In combination with any of the above embodiments, in an embodiment the apparatus may include a means for determining whether a mask bit is set to prevent a means for signaling of the numeric accumulation error and the means for signaling an exception based on the determination that the mask bit is not set and based on the determination that the numeric accumulation error occurred. In combination with any of the above embodiments, in an embodiment the apparatus may include a means for rounding the floating point result and a means for storing the rounded floating point result. The amount of precision lost in the mantissa of the floating point result may represent a percentage of bits in the mantissa of the floating point result that may be lost. The percentage of bits that may be lost may include a percentage of bits that may be lost when rounding the floating point result or a percentage of bits that may be lost when storing the rounded floating apparatus result. In combination with any of the above embodiments, in an embodiment the apparatus may include a means for determining a numeric accumulation error non-zero precision flag and a means for controlling whether to ignore at least one trailing bit of the mantissa with a value of zero. The means for determining the numeric accumulation error non-zero precision flag may be based on the instruction, a previous instruction, or a floating point control register. The means for controlling whether to ignore at least one trailing bit of the mantissa may use the numeric accumulation error non-zero precision flag. The means for computing the amount of precision lost in the mantissa of the floating point result may be based on the numeric accumulation error non-zero precision flag. In combination with any of the above embodiments, in an embodiment the apparatus may include a means for determining a numeric accumulation error non-zero precision flag and a means for controlling whether to ignore bits of the mantissa of the floating point result with a value of zero. The means for determining the numeric accumulation error non-zero precision flag may be based on the instruction, a previous instruction, or a floating point control register. The means for controlling whether to ignore at least one trailing bit of the mantissa may use the numeric accumulation error non-zero precision flag. The means for computing the amount of precision lost in the mantissa of the floating point result may be based on the numeric accumulation error non-zero precision flag. In combination with any of the above embodiments, in an embodiment the floating point result may be computed from source values and the instruction may be a fused multiply-add instruction. The means for executing the instruction may include a means for computing a sum based on the source values and a means for computing the floating point result based on the sum and at least one of the source values. 

What is claimed is:
 1. A processor, comprising: circuitry to decode at least one instruction, the instruction to compute a floating point result; an execution unit including circuitry to: execute the instruction to determine the floating point result; compute an amount of precision lost in a mantissa of the floating point result, the amount of precision lost corresponding to a plurality of bits lost in the mantissa of the floating point result; compare the amount of precision lost in the mantissa of the floating point result to a numeric accumulation error precision threshold; determine whether a numeric accumulation error occurred based on the comparison between the amount of precision lost in the mantissa of the floating point result and the numeric accumulation error precision threshold; and write a value to a flag for notification that the numeric accumulation error occurred, the value based on the determination that the numeric accumulation error occurred.
 2. The processor of claim 1, wherein: the execution unit further includes circuitry to determine the numeric accumulation error precision threshold based on the instruction, a previous instruction, or a floating point control register; and the comparison between the amount of precision lost and the numeric accumulation error precision threshold is based on the numeric accumulation error precision threshold that is determined.
 3. The processor of claim 1, wherein the execution unit further includes circuitry to: determine whether a mask bit is set to prevent signaling of the numeric accumulation error; and signal an exception based on the determination that the mask bit is not set and based on the determination that the numeric accumulation error occurred.
 4. The processor of claim 1, wherein: the execution unit further includes circuitry to: round the floating point result; store the rounded floating point result; and the amount of precision lost in the mantissa of the floating point result represents a percentage of bits in the mantissa of the floating point result that is lost, the percentage of bits that is lost includes: a percentage of bits that is lost when the floating point result is rounded; or a percentage of bits that is lost when the rounded floating point result is stored.
 5. The processor of claim 1, the execution unit further comprising circuitry to: determine a numeric accumulation error non-zero precision flag based on the instruction, a previous instruction, or a floating point control register; and control, using the numeric accumulation error non-zero precision flag, whether to ignore at least one trailing bit of the mantissa of the floating point result with a value of zero, wherein the computation of the amount of precision lost in the mantissa of the floating point result is based on the numeric accumulation error non-zero precision flag.
 6. The processor of claim 1, the execution unit further includes circuitry to: determine a numeric accumulation error non-zero precision flag based on the instruction, a previous instruction, or a floating point control register; and control, using the numeric accumulation error non-zero precision flag, whether to ignore bits of the mantissa of the floating point result with a value of zero, wherein the computation of the amount of precision lost in the mantissa of the floating point result is based on the numeric accumulation error non-zero precision flag.
 7. The processor of claim 1, wherein: the floating point result is computed from source values; the instruction is a fused multiply-add instruction; and the execution of the instruction includes circuitry to: compute a sum based on the source values; and compute the floating point result based on the sum and at least one of the source values.
 8. A method for detecting numeric accumulation error, comprising: decoding at least one instruction, the instruction for computing a floating point result; executing the instruction to determine the floating point result; computing the amount of precision lost in a mantissa of the floating point result, the amount of precision lost corresponding to a plurality of bits lost in the mantissa of the floating point result; comparing the amount of precision lost in the mantissa of the floating point result to a numeric accumulation error precision threshold; determining whether a numeric accumulation error occurred based on the comparison between the amount of precision lost in the mantissa of the floating point result and the numeric accumulation error precision threshold; and writing a value to a flag for notification that the numeric accumulation error occurred, the value based on the determination that the numeric accumulation error occurred.
 9. The method of claim 8, further comprising: determining the numeric accumulation error precision threshold based on the instruction, a previous instruction, or a floating point control register; and the comparison between the amount of precision lost and the numeric accumulation error precision threshold using the numeric accumulation error precision threshold that is determined.
 10. The method of claim 8, further comprising: determining whether a mask bit is set to prevent signaling of the numeric accumulation error; and signaling an exception based on the determination that the mask bit is not set and based on the determination that the numeric accumulation error occurred.
 11. The method of claim 8, further comprising: rounding the floating point result; storing the rounded floating point result; and the amount of precision lost in the mantissa of the floating point result representing a percentage of bits in the mantissa of the floating point result that is lost, the percentage of bits that is lost including: a percentage of bits that is lost when rounding the floating point result; or a percentage of bits that is lost when storing the rounded floating point result.
 12. The method of claim 8, further comprising: determining a numeric accumulation error non-zero precision flag based on the instruction, a previous instruction, or a floating point control register; and controlling, using the numeric accumulation error non-zero precision flag, whether to ignore at least one trailing bit of the mantissa of the floating point result with a value of zero, wherein the computation of the amount of precision lost in the mantissa of the floating point result is based on the numeric accumulation error non-zero precision flag.
 13. The method of claim 8, further comprising: determining a numeric accumulation error non-zero precision flag based on the instruction, a previous instruction, or a floating point control register; and controlling, using the numeric accumulation error non-zero precision flag, whether to ignore bits of the mantissa of the floating point result with a value of zero, wherein the computation of the amount of precision lost in the mantissa of the floating point result is based on the numeric accumulation error non-zero precision flag.
 14. An execution unit, comprising circuitry to: execute at least one instruction to determine a floating point result; compute an amount of precision lost in a mantissa of the floating point result, the amount of precision lost corresponding to a plurality of bits lost in the mantissa of the floating point result; compare the amount of precision lost in the mantissa of the floating point result to a numeric accumulation error precision threshold; determine whether a numeric accumulation error occurred based on the comparison between the amount of precision lost in the mantissa of the floating point result and the numeric accumulation error precision threshold; and write a value to a flag for notification that the numeric accumulation error occurred, the value based on the determination that the numeric accumulation error occurred.
 15. The execution unit of claim 14, the execution unit further comprising circuitry to determine the numeric accumulation error precision threshold based on the instruction, a previous instruction, or a floating point control register, wherein the comparison between the amount of precision lost and the numeric accumulation error precision threshold is based on the numeric accumulation error precision threshold that is determined.
 16. The execution unit of claim 14, further comprising circuitry to: determine whether a mask bit is set to prevent signaling of the numeric accumulation error; and signal an exception based on the determination that the mask bit is not set and based on the determination that the numeric accumulation error occurred.
 17. The execution unit of claim 14, further comprising circuitry to round the floating point result and store the rounded floating point result, wherein the amount of precision lost in the mantissa of the floating point result represents a percentage of bits in the mantissa of the floating point result that is lost, the percentage of bits that is lost includes: a percentage of bits that is lost when the floating point result is rounded; or a percentage of bits that is lost when the rounded floating point result is stored.
 18. The execution unit of claim 14, further comprising circuitry to: determine a numeric accumulation error non-zero precision flag based on the instruction, a previous instruction, or a floating point control register; and control, using the numeric accumulation error non-zero precision flag, whether to ignore at least one trailing bit of the mantissa of the floating point result with a value of zero, wherein the computation of the amount of precision lost in the mantissa of the floating point result is based on the numeric accumulation error non-zero precision flag.
 19. The execution unit of claim 14, further comprising circuitry to: determine a numeric accumulation error non-zero precision flag based on the instruction, a previous instruction, or a floating point control register; and control, using the numeric accumulation error non-zero precision flag, whether to ignore bits of the mantissa of the floating point result with a value of zero, wherein the computation of the amount of precision lost in the mantissa of the floating point result is based on the numeric accumulation error non-zero precision flag.
 20. The execution unit of claim 14, wherein: the floating point result is computed from source values; the instruction is a fused multiply-add instruction; and the execution of the instruction includes circuitry to: compute a sum based on the source values; and compute the floating point result based on the sum and at least one of the source values. 